Pump overrun is killing my heating!

[EvilDrPorkChop]

If there was no circuit you wouldn't of had flow. Did you have a bypass?

It would go round the LLH. That's effectively your bypass, plus an integrated one.

 

[milleniumaire]

If there was no circuit you wouldn't of had flow. Did you have a bypass?

The only bypass is the one in the boiler.

 

[SJB060685]

It would go round the LLH. That's effectively your bypass, plus an integrated one.

He said prior to the llh lol

 

[SJB060685]

There is a bypass in the boiler, but yeah the Vaillant controls usually hold the zone valve open for a period of time. Well they do on the newer system from what I recall.

I wish all boilers were this advanced lol

 

[milleniumaire]

It would go round the LLH. That's effectively your bypass, plus an integrated one.

Yes, in the new setup it can cycle to the LLH and back. If the external pump was on, it could cycle further (and cool down quicker, while at the same time continuing to provide heat - to the cylinder in the morning) and I guess this is the crux of the issue that this doesn't happen in pump overrun mode.

 

[EvilDrPorkChop]

Out of interest have you checked to see if there's power to the pump? I've had a couple of them newer UPM3s fail quite early on tbh.

 

[milleniumaire]

Out of interest have you checked to see if there's power to the pump? I've had a couple of them newer UPM3s fail quite early on tbh.

Yes, there's definitely power as the LEDs are on and I can feel the pump vibrating, which increases as I increase the speed.

 

[EvilDrPorkChop]

Yes, there's definitely power as the LEDs are on and I can feel the pump vibrating, which increases as I increase the speed.

I meant when it isn't running and the boiler is saying it should be.

 

[milleniumaire]

I meant when it isn't running and the boiler is saying it should be.

Ah, sorry, I see what you mean.

The only situations I'm aware of where the external pump doesn't start, when the internal pump does start is S.0 and S.7. It is possible there are other status codes that I haven't come across, but these are the two I regularly see.

However, when there's demand and neither of the above status codes are showing on the boiler, then both pumps are on at the same time.

 

[EvilDrPorkChop]

Ah, sorry, I see what you mean.

The only situations I'm aware of where the external pump doesn't start, when the internal pump does start is S.0 and S.7. It is possible there are other status codes that I haven't come across, but these are the two I regularly see.

However, when there's demand and neither of the above status codes are showing on the boiler, then both pumps are on at the same time.

Ah right OK, as I said in an earlier post then i'd configure your HW configuration correctly on the PCB first and see if that makes a difference. You're probably getting a lot of anti cycling.

 

[EvilDrPorkChop]

Yes, the system has always been setup for DHW priority.

D.75 = 45 (factory setting)
D.77 = 37 (factory default and maximum output I believe)
D.78 = 80 (factory default)

So, it looks like these settings are all defaults.

Yes, the cylinder temperature probe has been connected to S9 on the VR 71 wiring centre as shown in the attached schema diagram. This diagram was supplied by Vaillant as the nearest to my setup as none of the diagrams in the VRC 700 System Diagrams booklet were any good! However, this diagram shows each zone has having its own pump (and mixing valve), which isn't the case in my system.

Can I just ask, who did that drawing for you? It's great, I struggle to get an answer for basic things out of my rep (Although he isn't bad to be fair).

 

[milleniumaire]

Can I just ask, who did that drawing for you? It's great, I struggle to get an answer for basic things out of my rep (Although he isn't bad to be fair).

I don't think Vaillant created that drawing especially for me. If you look at the date, it is 30/07/2018.

The VRC 700 came with a printed System diagram book, unfortunately none of the diagrams seemed to come close to matching my setup and I pointed this out to Vaillant when asking them to check the installation for me (via email) as I wasn't 100% convinced that everything had been connected up correctly by the heating engineer. He's a great guy and does all my servicing and upgrading, but even he admits its difficult to keep up with technology! As an IT consultant, I'm used to getting into the detail and like to understand how things work, so had no problem liaising with Vaillant support and have made a couple of changes as a result.

As I explained earlier, although the diagram reflects the zones I have (DHW via cylinder, 2 x UFH and radiators) there are some differences, mainly in the area I'm having issues; the external pump. The diagram shows each zone having its own pump, so I suspect these would be wired up in the same way as the zone valves so that when the valve opens the pump switches on. It appears to be a little more complicated to use a single pump for all zones and even my engineer was surprised that the pump had to be connected to the boiler, rather than to the wiring centre!

One day, when I have time, I may create my own schema diagram using Microsoft Visio 😀

 

[milleniumaire]

Just found the installation guide for the X40 expansion board, which plugs into the boiler PCB and provides for the external pump connection.

Here are the relevant pages:

I'm trying to understand how the above relates to the actual device and the way the pump has been wired upto it:

On the boiler d.27 = 5 and d.28 = 2

What's the difference between "Circulation pump", "External Pump" and "Storage charging pump"?

Based on the photo, showing the pump is connected to the yellow "rel 1" connectors, which 1, 2, 3, 4, 5 or 6 does this relate to?

Because it is wired to rel 1 (open) and d.28 is 2, I assume it relates to 2 in the table. Are 1 and 2 mutually exclusive. 1 shows a ZP & tap and 2 shows a radiator, so I'm thinking they relate to DHW and heating! I'm not sure what "ZP" means.

Note: Just realised the last paragraph is nonesense as d.28 relates to "rel 2", so I'm now wondering if either the connection is wrong or the setting of d.27 is wrong!

 

[ShaunCorbs]

Those connections need to be done better as there’s cores nearly touching each other

 

[SJB060685]

As shaun says those connections are poor and the chance of a short circuit are real. Looking at the amendment should external pump go to relay 2?

 

[EvilDrPorkChop]

Just found the installation guide for the X40 expansion board, which plugs into the boiler PCB and provides for the external pump connection.

Here are the relevant pages:

View attachment 46989

View attachment 46991
I'm trying to understand how the above relates to the actual device and the way the pump has been wired upto it:

View attachment 46990

On the boiler d.27 = 5 and d.28 = 2

What's the difference between "Circulation pump", "External Pump" and "Storage charging pump"?

Based on the photo, showing the pump is connected to the yellow "rel 1" connectors, which 1, 2, 3, 4, 5 or 6 does this relate to?

Because it is wired to rel 1 (open) and d.28 is 2, I assume it relates to 2 in the table. Are 1 and 2 mutually exclusive. 1 shows a ZP & tap and 2 shows a radiator, so I'm thinking they relate to DHW and heating! I'm not sure what "ZP" means.

Note: Just realised the last paragraph is nonesense as d.28 relates to "rel 2", so I'm now wondering if either the connection is wrong or the setting of d.27 is wrong!

Should be down as external pump I think.

 

[milleniumaire]

Should be down as external pump I think.

So, assuming external pump is correct, does the chart suggest it can be wired in either of two different ways:

a. Connect to rel 2 and set d.28 to 2
b. Connect to rel 1 and set d.27 to 2

I'm concerned about the distinction between "circulation pump" (1) and "external pump" (2). Does this imply the pump will only work during hot water demand (1) or heating demand (2), but not both?

 

[SJB060685]

Your observation is like mine. Possibly connect to relay 2 and set to D.28 and see what happens?

 

[John.g]

Following this very interesting thread.
Just a few basic observations.
Pump overrun should not occur unless CH and/or HW satisfied, if boiler output still too high on max turndown then burner off but boiler circ pump and secondary pump should continue to run but overrun should not be called for. When pump overrun is called for normally, would expect secondary pump to be off. Suggest to check if pump overrun comes on with burner off with call from CH or HW.
Slow rad heat up/output not mentioned but with a LLH the boiler circ pump and external pump should be matched with boiler circ pump flowrate slightly higher?. so possibly wrong settings with boiler circ pump or more likely secondary pump or faulty pump. Also assume LLH connections correct.

 

[John.g]

Also S.0 refers to "no heating demand" which I would think is indicative of the boiler sensing no heat demand even with zone valve(s) open, I would have a good look at that Grundfos Pump as it may be the main cause of your problem, hopefully.

 

[ShaunCorbs]

Also don’t forget about if there’s flow through the pump the leds will light up as the unit is acting like a generator eg there’s no power going to the pump plug

 

[milleniumaire]

Good morning. Just catching up on the new posts.

Also don’t forget about if there’s flow through the pump the leds will light up as the unit is acting like a generator eg there’s no power going to the pump plug

Shaun, are you saying the LED's on the pump would still work even if the pump didn't have power? When I press the speed button on the front of the pump, I can hear/feel the pump toggling through the different speeds. Also, if the pump wasn't working, surely the radiators/UFH and hot water would never warm up as there's no way the internal boiler pump could push water past the LLH and around the system!

Also S.0 refers to "no heating demand" which I would think is indicative of the boiler sensing no heat demand even with zone valve(s) open, I would have a good look at that Grundfos Pump as it may be the main cause of your problem, hopefully.

Given my comments above about the pump and the fact that I've done tests on each thermostat to force demand for each zone and can see the pump LED's turning on/off as demand is requested/removed, I'm feeling very confident the external pump is working. Whether it is connected and configured correctly is another matter!

Following this very interesting thread.
Just a few basic observations.
Pump overrun should not occur unless CH and/or HW satisfied, if boiler output still too high on max turndown then burner off but boiler circ pump and secondary pump should continue to run but overrun should not be called for. When pump overrun is called for normally, would expect secondary pump to be off. Suggest to check if pump overrun comes on with burner off with call from CH or HW.
Slow rad heat up/output not mentioned but with a LLH the boiler circ pump and external pump should be matched with boiler circ pump flowrate slightly higher?. so possibly wrong settings with boiler circ pump or more likely secondary pump or faulty pump. Also assume LLH connections correct.

So, I set the heating and hot water to start at 06:30am this morning, which is half an hour later than I usually set it, but I wanted to monitor what happened. At 07:00am the system was still heating the cylinder. The external pump was on, the system status (via the VRC 700) was showing DHW and the boiler status was S.24 (Burner ignited), so all looked to be okay, apart from that fact that the cylinder was still not to temperature (65 degrees C) after 30 minutes. There was absolutely no heat in the radiators or UFH.

10 minutes later it was showing S.20 (Warmstart demand). At 1 hour since turning on I noticed it had switched to heating demand and the radiators finally started to warm up.

I confess, I didn't see any sign of pump overrun this morning. Maybe I just didn't look at the right time (in the first 30 mins) or maybe I'm mistaken about this. However, should it really take an hour to heat up the water in a 260 litre Vaillant unistor cylinder?

Looking at the current config of the external pump. It is currently wired to rel 1 (open) and according to the chart, this suggests that d.27 determines what will happen. As this is currently set to 5, the chart says "External gas valve" for this value. I wonder if this is just incorrectly set and the engineer set d.28 to 2 when he meant to set d.27 to 2 as according to the chart, d.28 has no effect unless the pump is connected to rel 2 (open). As far as I'm aware, my system doesn't have an "External gas valve", so I'm not sure how this impacts on the pump starting/stopping.

From my observations yesterday (not this morning) it appeared that whenever the gas burner was on, the external pump was on. So, when in pump overrun mode, the gas burner wasn't on and therefore the external pump wasn't on. Again, this could be a complete red herring, but I'm trying to make sense of the current configuration and what is happening, given the fact that setting 5 for d.27 mentions "gas valve".

As the pump cable connections are inside the boiler, I don't want to take the front off to change them, so it may be better for me to simply change d.27 to value 2, rather than 5 and see what impact (if any) that has.

I appreciate the connections need to be re-done and I'll ask the engineer to look at them as he's due back soon to service the boiler.

So, although I didn't see any evidence of pump overruns this morning, I've definitely seen it happening on other days, so I'm not ruling this out completely just yet.

If it is expected to take an hour to heat the cylinder to 65 deg C then it would appear everything is working as normal and I'll just have to turn on the hot water earlier in the morning to give this time to happen, followed by time to heat up the house. However, this never used to be a problem prior to the recent upgrade, when the heating/hot water started up at 06:00 every morning and the house was toasty by the time I got out of bed at 07:00am.

 

[Murdoch]

What happens if you set the water to run more than an hour before the heating comes on? i.e. allow the water to run and then turn off before running the heating?

 

[milleniumaire]

Following this very interesting thread.
Just a few basic observations.
Pump overrun should not occur unless CH and/or HW satisfied, if boiler output still too high on max turndown then burner off but boiler circ pump and secondary pump should continue to run but overrun should not be called for. When pump overrun is called for normally, would expect secondary pump to be off. Suggest to check if pump overrun comes on with burner off with call from CH or HW.
Slow rad heat up/output not mentioned but with a LLH the boiler circ pump and external pump should be matched with boiler circ pump flowrate slightly higher?. so possibly wrong settings with boiler circ pump or more likely secondary pump or faulty pump. Also assume LLH connections correct.

Sorry, I meant to comment on your post.

Regarding matching the flowrates for the boiler and external pumps, the external Grundfos pump has a touch button that allows me to increase/decrease the flowrate and it is currently on minimum. I'm not sure exactly how the flow rate of the internal pump is controlled, possibly through a boiler config parameter, but I seem to recall it being on a low setting.

When you say assume LLH connections correct, I assume you are referring to flow and return connections to the system and boiler? With my basic knowledge they appear to be correct and I know my engineer has fitted this type of LLH before, so I would hope he got it right. If they weren't connected up correctly, I'm sure I would be seeing other, more obvious issues, such as heating zones not warming up etc.

I think I understand what you are saying about pump overrun. Basically, you wouldn't expect the external pump to be turned on when pump overrun is on. This is what I am seeing. Usually, when the boiler shows 2.7 (pump overrun) the burner symbol (hour glass) is NOT displayed.

 

[milleniumaire]

What happens if you set the water to run more than an hour before the heating comes on? i.e. allow the water to run and then turn off before running the heating?

Do you mean set the timer to stagger the start times for hot water and heating, so:

06:00 Water on
07:00 Water off
07:10 Heating on

I would expect the hot water demand to end before 07:00 i.e. boiler and pump turn off, due to the cylinder reaching the required temperature. This morning, the heating demand started around 55 mins after the hot water demand started, suggesting it took 55 minutes to heat up the 260 litre cylinder.

If I've understood you correctly, I'm not sure what this would prove.

I have wondered it it is possible to change the settings so that hot water does NOT have priority i.e. heat up both the cylinder and radiators/UFH at the same time?