Pump overrun is killing my heating!

[EvilDrPorkChop]

Thermostatic control should give very tight control, I have one on my HW cylinder set to 60C, and it controls to within a few degrees of this from a HW cylinder temp of 85C (summer solar) to 65C from oil fired boiler.

I was more meaning the HW at the Top of the cylinder is more likely to be nearer 70oc, rather than the 65oc at the bottom of the cylinder where the probe is located.

 

[milleniumaire]

There's three things it could be;

1 - Something back feeding - shower or mixer tap.
2 - Your incoming PRV on the cold main has failed and letting too much pressure through.
3 - Turning up your cylinder to 65oc has knackered the cartridges in on the two older Mira Excels (Had this before on other makes) Max input on showers is 65oc and it's probable your HW was nearer 70oc. The easiest way to check is whether your Digital shower is still outputting the same temp on the same setting.

I'd be going with option 3 tbh if everything else seems OK.

After your post and assuming the worst, I've just spent some time testing both Mira showers. There's a definite range of cold to hot when turning the temperature control, so they appear to be working fine, it's just that the "hot" setting is now around 9 when it used to be 5.

It reminded me that it's possible to change these, so out with the screwdriver and I took the front of the dial off and adjusted it, so now it is in position 5 at the expected shower temperature rather than at 8. Both showers temperature settings now seem to be around where they used to be!

Unfortunately, the new digital shower hasn't been used yet (apart from testing) as we are still awaiting the new shower enclosure, which won't be in stock until February.

So, with the water temp now set to 60 deg C and the shower temp gauges adjusted, things should be back to normal, assuming the hot water takes less than 30 minutes to heat up in the morning, allowing at least 30 mins to start warming up the house (boiler is timed to come on an hour before we get up).

Interestingly (or not), after testing the showers, I noticed the system was in DHW mode (not surprisingly), but the boiler was showing status S.53 (Appliance is within the waiting period of the operation block function due to water shortage (VL-RL spread too big). I haven't noticed this one before. Everything still seemed to be working as normal (external and boiler pump on, cylinder valve open, gas burner on).

Went back to the boiler 10 minutes later and it was showing S.31 (Central heating thermostat knob turned off or no heat demand by the eBUS control unit). Again, not seen this before! At this point nothing is on, but that's not surprising as according to the VRC 700 the system is in standby as there's no demand for heating or hot water. Ah well, I'll assume all is well as this is obviously a "status" code, not an "error" code.

 

[John.g]

In my case the solar coil is in the bottom of the cylinder so the whole cylinder heats to up to 85C at times before cylinder & collector protection operates.
I noticed the OPs was 73C at the top and 65C at the bottom. With a normal gas/oil fired cylinder coil with the flow from top to bottom one might expect to see the temperature higher in the cylinder top than at the sensing point, I have a good few PT1000 sensors in dry pockets on my cylinder but I've always found it strange that the cylinder heats up almost completely uniformly from top to bottom with only a few degrees difference, say 3C max. If I start running off hot water at a few LPM with boiler still firing then the top is ~ 5C higher than the other sensors. coil flow temp is 75C.

 

[EvilDrPorkChop]

After your post and assuming the worst, I've just spent some time testing both Mira showers. There's a definite range of cold to hot when turning the temperature control, so they appear to be working fine, it's just that the "hot" setting is now around 9 when it used to be 5.

It reminded me that it's possible to change these, so out with the screwdriver and I took the front of the dial off and adjusted it, so now it is in position 5 at the expected shower temperature rather than at 8. Both showers temperature settings now seem to be around where they used to be!

Unfortunately, the new digital shower hasn't been used yet (apart from testing) as we are still awaiting the new shower enclosure, which won't be in stock until February.

So, with the water temp now set to 60 deg C and the shower temp gauges adjusted, things should be back to normal, assuming the hot water takes less than 30 minutes to heat up in the morning, allowing at least 30 mins to start warming up the house (boiler is timed to come on an hour before we get up).

Interestingly (or not), after testing the showers, I noticed the system was in DHW mode (not surprisingly), but the boiler was showing status S.53 (Appliance is within the waiting period of the operation block function due to water shortage (VL-RL spread too big). I haven't noticed this one before. Everything still seemed to be working as normal (external and boiler pump on, cylinder valve open, gas burner on).

Went back to the boiler 10 minutes later and it was showing S.31 (Central heating thermostat knob turned off or no heat demand by the eBUS control unit). Again, not seen this before! At this point nothing is on, but that's not surprising as according to the VRC 700 the system is in standby as there's no demand for heating or hot water. Ah well, I'll assume all is well as this is obviously a "status" code, not an "error" code.

Your showing S.53 because of the output still being 37kw, have you rated this down to 22kw on D. Setting on the PCB?

 

[EvilDrPorkChop]

In my case the solar coil is in the bottom of the cylinder so the whole cylinder heats to up to 85C at times before cylinder & collector protection operates.
I noticed the OPs was 73C at the top and 65C at the bottom. With a normal gas/oil fired cylinder coil with the flow from top to bottom one might expect to see the temperature higher in the cylinder top than at the sensing point, I have a good few PT1000 sensors in dry pockets on my cylinder but I've always found it strange that the cylinder heats up almost completely uniformly from top to bottom with only a few degrees difference, say 3C max. If I start running off hot water at a few LPM with boiler still firing then the top is ~ 5C higher than the other sensors. coil flow temp is 75C.

Mine heats up fairly uniform too, however mine is only a 170l. I find that when you get over 200l you get the difference, the top being hotter, really you should probably need a destrat pump. I also find you find it worse with a higher flow temp, like on HW priority. This is where a circulating return, tee'd into the cylinder Inlet works quite well.

 

[milleniumaire]

Your showing S.53 because of the output still being 37kw, have you rated this down to 22kw on D. Setting on the PCB?

Okay, thanks, that actually makes me feel a little better - knowing its likely to be a config issue rather than a fault somewhere. As it's a boiler setting, I guess this parameter must have always had that value and it isn't something that would change with the upgrade of controller from VRC 430 to VRC 700.

I haven't changed this setting as this is one of the many questions I've put to Vaillant technical support (showing them what the current settings are and asking them to advise on the best values). Unfortunately, I haven't yet received a response.

 

[EvilDrPorkChop]

Okay, thanks, that actually makes me feel a little better - knowing its likely to be a config issue rather than a fault somewhere. As it's a boiler setting, I guess this parameter must have always had that value and it isn't something that would change with the upgrade of controller from VRC 430 to VRC 700.

I haven't changed this setting as this is one of the many questions I've put to Vaillant technical support (showing them what the current settings are and asking them to advise on the best values). Unfortunately, I haven't yet received a response.

Personally, if I was configing your system. I'd set -
HW Target Temp on 55oc
D.20 - 60oc
D.72 - 120
D.75 - 45 mins
D.77 to 22kw
D.78 to 80oc

D.19 - 3 (Always Speed 2)

 

[John.g]

Just had a response from Vaillant technical support regarding one of my emails and their response is that I need to wire the external pump upto the VR 71 wiring centre! The exact opposite of what they told my heating engineer. I'm taking this with a pinch of salt as at the time I emailed them I wasn't aware that the value of d.27 was 5 and they have assumed it is 2 (apparently this is the default). Also, they are telling me that a value of 2 means the external pump would NOT work during DHW mode and so if using the VR 40 to connect up the pump, I would need to connect a SECOND external pump to relay 2 and set d.28 to 3. The fact that I'm seeing the external pump work in both DHW AND heating mode doesn't match what they are telling me, possibly due to the d.27 value of 5 (I've now asked them about this).

So, currently, they are telling me I either have to wire the pump upto the VR 71 or get a second pump, which I believe is overkill for my system. I'm still waiting for answers to a number of questions I asked yesterday.

Based on feedback so far I think I need to investigate the DHW 2 port value to make sure it is functioning correctly. If this isn't fully opening then even if the pump is running I guess the flow wouldn't go anywhere, but then I would assume the cylinder water would never get hot, which it clearly is (eventually).

Reducing the cylinder temperature setting may help the situation, so I've now reduced it to 60 deg C and I will monitor the impact in the morning and also try to determine what the start temperature of the cylinder is before it starts being heated.

I'm still on the fence about the pump wiring/configuration, but wouldn't be surprised if there was potentially an issue, even though the pump always seems to come on when the gas burner is on i.e. when there is demand from one of the zones/DHW.

As far as pump overrun goes, I'm not really seeing that as much as I expected to, so although that is the subject line for my post, it may be a red herring! I still can't help thinking it would be better if the external pump was on during pump overrun, providing at least one of the zone valves was open. Maybe this doesn't happen as pump overrun tends to happen when the heating demand has been met and it is cooling down the water temperature in the boiler to protect the heat exchanger, so to continue to pump hot water around the system might increase room/cylinder temperatures beyond what was desired? Just a thought.

Back to basics for me.
Is there a clue in the label re UPS3 connection to VR 71 as they suggest, above.
TITLE 12-37kW, Low Loss Header, DHW (Secondary Circulation), 1 UFH Zone (3rd Party), 2 Radiator Zones (Wired or Wireless VRC 700, VR91)

Why not connect a indicating light between L/N in R4 where it says DHW Secondary Circulation and observe it, if it always lights up and goes out with boiler circ pump operation in both CH & HW mode , then maybe that's where the UPS3 should be connected?.
Also if boiler circ pump on and R4 "on" with UPS3 off then maybe another clue that it should be connected in to R4.

 

[John.g]

Don't think R4 is correct, that seems allocated to a cylinder secondary recirc pump.

 

[milleniumaire]

Back to basics for me.
Is there a clue in the label re UPS3 connection to VR 71 as they suggest, above.
TITLE 12-37kW, Low Loss Header, DHW (Secondary Circulation), 1 UFH Zone (3rd Party), 2 Radiator Zones (Wired or Wireless VRC 700, VR91)

Why not connect a indicating light between L/N in R4 where it says DHW Secondary Circulation and observe it, if it always lights up and goes out with boiler circ pump operation in both CH & HW mode , then maybe that's where the UPS3 should be connected?.
Also if boiler circ pump on and R4 "on" with UPS3 off then maybe another clue that it should be connected in to R4.

Hi John, I understand what you are suggesting, but as things stand I/the engineer have received different advice from different Vaillant support people, so I need to understand why they are making these different suggestions, hopefully once they respond to my email.

What they actually told me in the last email was:

"I would advise to remove the VR40 and wire the single system pump as shown in the example diagram below with a permanent 230V supply to the grey wires and use the oranges from all zone valves wired to the pump live."

So, they are essentially wanting to turn the external pump on and off whenever any of the zone valves open or close, which I believe is what the engineer was originally considering doing, but then got confused looking at the schema diagram they had supplied (see attached) and called Vaillant, who told him he needed to use the VR 40, which he then ordered and installed the following day!

It's an interesting thought about using R4 for the external pump, however in the schema diagram it does appear to be associating R4 with the cylinder, so my gut feeling is it is likely to only operate in DHW mode, but as you say it may be worthwhile testing it, but I'll wait until I have more clarity from Vaillant. Maybe they'll suggest yet another way of wiring up the pump 😀

EDIT: Just seen your post from 11:36 last night, so it appears we agree about R4.

 

[John.g]

"I would advise to remove the VR40 and wire the single system pump as shown in the example diagram below with a permanent 230V supply to the grey wires and use the oranges from all zone valves wired to the pump live."

That is the normal S plan configuration, there is a permanent live to one side of the zone valve end switches and all the wires (switched live) from the other end(s) are marshalled together to provide a a run signal to the boiler which now normally controls the boiler circ pump, so if any one, or all, zone valves are open then the boiler has a run signal and when all zone vales are shut then no run signal, I suppose with all their fancy control systems now, they don't use the end switches now but employ some virtual means of determining this hence all these status alerts or whatever.
It's a bit surprising that there is no contact on the boiler from the circ pump run signal, there must be some means of picking up this and wiring it via a external relay (if required) to run the external pump, I think this was suggested previously, above. Also, this implies that the (a) zone valve is kept open for the duration of any pump overrun, oh no, the pump won't run unless a zone valve is open!.

 

[milleniumaire]

Got up early this morning, prior to the heating/hot water turning on at 6:30am, so I could monitor temperatures etc.

Took readings before the boiler started up. This showed the current cylinder temperature was 56 deg C (the desired setting is 60). So, 4 deg C heat loss over 7.5 hours, which seems much better than the other night 😀

When the boiler started up it went straight into heating mode, I guess because 56 is within 5 of 60, so no need to heat up the cylinder.

Had a shower then re-checked at 06:55 and the boiler was now heating up the cylinder, which it did within about 10 mins as by 7:10 it was back to heating mode.

So, everything worked perfectly, even the shower controls! Had a chat with my son and he admitted he had been having late night showers every 2 or 3 days!!!!!! If only I had known that.

It would therefore appear that a combination of the cylinder temp being set to 65 and my son's late night, secret showers using up hot water are possibly the reasons for the cylinder taking so long to heat up in the morning.

Obviously, there are still settings to change and possibly wiring to change, or at least an explanation of the wiring settings, so I await feedback from Vaillant, but it would appear the "pump overrun" situation I thought was occurring is a red herring! I'll update when I hear from Vaillant.

 

[John.g]

It would b interesting during the day to run off some hot water until the system changes over to HW, then stop running off the hot water and monitor the exact time taken to reach cut off at 60C, also a full set of readings during its run including cylinder top and target temperatures, LLH temperatures etc, can then tell pretty exactly the performance of the cylinder "coil" and might then be able to understand why it should take so long to reach 65C, if required.

 

[milleniumaire]

It would b interesting during the day to run off some hot water until the system changes over to HW, then stop running off the hot water and monitor the exact time taken to reach cut off at 60C, also a full set of readings during its run including cylinder top and target temperatures, LLH temperatures etc, can then tell pretty exactly the performance of the cylinder "coil" and might then be able to understand why it should take so long to reach 65C, if required.

Rather than wasting hot water (I am Yorkshire after all), I'll wait until my son has his next shower and take some readings. He has now agreed to always shower before 22:00pm in future!

I don't understand how the system gets the "Cyl temp top" reading. As far as I'm aware, there's only one temperature sensor in the cylinder, wired into the VR 71 and this shows the "Current cyl. temp". As you can see below from the VRC 700 settings, the "Cyl temp top" is shown within the Buffer cylinder menu. The "Cyl temp bottom" has NEVER shown a value. So how does the VRC 700 get the value for "Cyl temp top"?

 

[John.g]

Don't know but in post #77 it was 73c and now showing 68C so must be sensing it somewhere?. a bottom temperature if available would reflect the mains temperature in general and the current cylinder temperature where the sensor is would normally be located maybe 100/150mm above the cylinder coil return as you require the reheat process to begin when a small vol of hot water is drawn off . you will, in any case have a almost full cylinder of hot water available at the target temperature.

 

[milleniumaire]

Don't know but in post #77 it was 73c and now showing 68C so must be sensing it somewhere?. a bottom temperature if available would reflect the mains temperature in general and the current cylinder temperature where the sensor is would normally be located maybe 100/150mm above the cylinder coil return as you require the reheat process to begin when a small vol of hot water is drawn off . you will, in any case have a almost full cylinder of hot water available at the target temperature.

Yes, the top cylinder temperature figure does seem to vary.

There are no other cables from the cylinder to either the wiring centre or the boiler, apart from the temperature sensor that is wired into the VR 71.

Another question for Vaillant technical support I think as it would be useful to understand the origin of this VRC 700 menu option. Possibly also, why is there a top temperature value and not a bottom temp setting.

 

[John.g]

With no cylinder sensor the closest temperature to it is the boiler flow temperature, if so, on change over from HW to CH, it should drop very rapidly.

 

[Ben-gee]

I imagine that the bottom cylinder temperature is available from some cylinders - but not the one you have.

 

[milleniumaire]

Hi John, I understand what you are suggesting, but as things stand I/the engineer have received different advice from different Vaillant support people, so I need to understand why they are making these different suggestions, hopefully once they respond to my email.

What they actually told me in the last email was:

"I would advise to remove the VR40 and wire the single system pump as shown in the example diagram below with a permanent 230V supply to the grey wires and use the oranges from all zone valves wired to the pump live."

View attachment 47032
So, they are essentially wanting to turn the external pump on and off whenever any of the zone valves open or close, which I believe is what the engineer was originally considering doing, but then got confused looking at the schema diagram they had supplied (see attached) and called Vaillant, who told him he needed to use the VR 40, which he then ordered and installed the following day!

It's an interesting thought about using R4 for the external pump, however in the schema diagram it does appear to be associating R4 with the cylinder, so my gut feeling is it is likely to only operate in DHW mode, but as you say it may be worthwhile testing it, but I'll wait until I have more clarity from Vaillant. Maybe they'll suggest yet another way of wiring up the pump 😀

EDIT: Just seen your post from 11:36 last night, so it appears we agree about R4.

Just received the following confirmation from Vaillant regarding the wiring of the external pump:

"With D.27 set to 5 the external pump will only run when the burner is on for DHW or CH as this is for an external solenoid valve so when the burner switches off so does the external pump which does not allow for any pump over run.

The number 5 setting in D.27 external solenoid valve I have only used for a commercial application with an external gas solenoid valve or it has been used for a commercial application when a building management system requires a run and fault indicator. I asked my manager if he new of anyone in or outside technical that would use number 5 for an external pump, which he did not.

I think the best and only option is to disconnect the external pump from the VR40 and use the orange wires from all the zone valves to activate the single pump, this will ensure the pump continues to run all the time each zone valve is open.

I apologise for the conflicting information however the diagram shown below is the standard Vaillant diagram to control a single external system pump the system side of a LLH."

They have included the same diagram as before.

Very frustrating! Not only did I have to purchase a VR 40, but I had to pay the engineer to come back the following day and fit it and now I'll have to pay him to come out, remove it and rewire the pump - in the way he was originally going to wire it until told differently by Vaillant. They really should be accountable when they give bad advice!

One thing that confuses me about the diagram. I assume the SYS.FLOW is the external pump and this clearly shows the live wire from each of the heating zones (and the DHW, which isn't applicable in my case) being used to switch the live on the pump, but where are the neutral and earth wires for the pump connected? I assume my heating engineer would know this, or would he need to call Vaillant again, for yet more bad advice?

 

[John.g]

It should be easy enough to pick up a N&E somewhere, I wonder what logic the boiler uses to determine if any of the zone valves are open if it doesn't get a input back from them?. Why do you say ("and the DHW, which isn't applicable in my case)", don't you need a feed back from the orange wire on that Mot.valve as well.?

 

[milleniumaire]

It should be easy enough to pick up a N&E somewhere, I wonder what logic the boiler uses to determine if any of the zone valves are open if it doesn't get a input back from them?. Why do you say ("and the DHW, which isn't applicable in my case)", don't you need a feed back from the orange wire on that Mot.valve as well.?

Of course, you are correct. For some reason I was thinking the DHW symbol was for a circulation pump, but it is obviously for the cylinder zone valve, so yes, the live from R6 would also need to be included.

Couldn't resist taking the front off the VR 71 wiring centre to see what the engineer had done with the orange wires. He' has simply cut them off as only the brown, blue and green/yellow wires are connected for the Honeywell zone valves. Also, the two UFH thermal valves only have brown and blue wires, plus the cable from a more remote zone valve is only 3 core, even though the zone valve itself has more cores than this (they have also been cut off).

So, it would appear the instructions to connect up the orange wires won't work! What is the difference between the orange wire and brown live wire? Is it that the orange is switched live (whenever the brown is live)? In which case it looks like it can't be done for my setup due to the UFH valves not having a switched live wire!

 

[ShaunCorbs]

Yes when port valves are open the oranges become live on 2 ports

 

[milleniumaire]

Yes when port valves are open the oranges become live on 2 ports

So somehow, he would need to connect the brown cables to the live on the pump, but this doesn't seem to be possible without each zone valve causing all the others to open i.e. if all the live connections are connected together to the pump live!

Sounds like maybe an electrician and some sort of device that mimics the "switch live" functionality for the two UFH thermal valves would be required to achieve this, rather than my heating engineer?

Or, as I think you were alluding to in your earlier message, is there a relay or something on the wiring centre that could be used for the pump? If so, I would have thought Vaillant would have mentioned it.

 

[ShaunCorbs]

Pump normally is connected to the oranges I think basically your turning your system into an s plan

 

[John.g]

No, not the brown, the orange wires, are you sure those actuators had orange wires as I think you could, in some cases buy them with no end switches/orange wires.
Why don't you get back to them and ask them can they give you any contact on the boiler from its own circ pump, all you need then is a external relay to switch your UPS pump, there has to be a switched wire to the internal pump in the boiler, surely it should be easy enough to wire into this??, even though the UPS will also run then if/with pump overrun it doesn't matter as it wont deadhead and will just circulate water in its own half of the LLH.