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Discuss Pump overrun is killing my heating! in the Central Heating Forum area at Plumbers Forums
I could get the engineer back, but to what end? He has setup the system as it is, to the best of his knowledge, and it doesn't appear to be working "as well" as it used to be before the upgrade. I know he was on the phone to Vaillant at least three times while setting it up, which doesn't exactly inspire me with confidence! It is possible that introducing the LLH, external pump, VR 71 wiring centre and new VRC 700 controller has changed the way it works such that it doesn't work "as well" as it used to and I'll just have to accept that.run the water at 5am ******.
Water heating is generally "slower" if the system is also doing radiators if I recall things correctly
I must admit I'm a bit puzzled by the depth you are going to - can't you just get the engineer back?
Yes, I can see this through the analogue temp gauges I have on the pipes. The photos I've posted don't show that I have also fitted a couple of gauges to the boiler flow and return as well, so I now have 4 gauges showing the temps between the boiler and LLH and the LLH and system circuit. You are correct, the flow and return around the system, from/to the LLH are always slightly lower than those on the boiler side, but I wouldn't have thought they were low enough to make a huge difference.Before installing the LLH the system flow temperature would always be the same as the boiler flow (setpoint) temperature but with the LLH, depending on (any) mixing then the system flow temperature may be lower but easy to see this by your temperature gauges.
Sorry John, I'm not sure what you mean by setpoint.Is the boiler setpoint 75C ?, and was it the same prior to changes?. if the system flow temp never reaches 65C then it doesn't matter how long the boiler is on as the cylinder will never reach its SP, you could temporarily reduce it to say 55C.
Also most rapid heat recovery coils are designed with flow temperatues of up to 85C and with very high circulation rates to get their rated output.
Yes, the system does use weather compensation and each zone has its own heat curve. While this is supposed to make the system more efficient, it also makes it more difficult to understand what or why things are happening e.g. why is there no heat demand for a zone when the desired temp is set to 21 and the current temp for the zone is showing 19 and the rooms are cold!It seems that this controller, for whatever reason is telling your boiler to run at 58C, based on this and your return temps and assuming room temperatures of 20C then these rads will only be emitting 56% of their rated output which would account for the slow heat up. This controller may be some smart form of outside temperature compensation, must have a read up of it.
I just beat you to posting!Just had a quick scan through it and it does compensate for the outside air temperature with a outside temperature sensor, you can see on page 12 that you can change the heating curves, for example if currently set on curve 2, it will call for a boiler SP (reqrired boiler temperature) of 65C at OT of 0C, 55C at 5C, and 45C at 10C. If you select heating curve 2.5 then the numbers are 73C at 0C, 63C at 5C, and 52C at 10C and so on. The HW required temperature seems to be set by default to 60C but don't see any corresponding boiler SP, if working properly, I would expect to see the boiler SP temperature rising with the actual cylinder temperature. You obviously need a cylinder sensor connected.
It's a 260 litre Vaillant unistor unvented cylinder.What size is the cylinder, 65oc seems a high set point tbh and may explain your reheat issues in the morning.
The Vaillant system has an Anti Legionella Setting that you can turn on, personally 60oc is too hot for me mines set at 55oc. I'd be careful as many showers have a Max inlet temp of 65oc also, so if your probe is measuring 65oc at the bottom it'll be more like 70oc at the top of the cylinder.It's a 260 litre Vaillant unistor unvented cylinder.
60 Deg C is obviously the lowest setting to avoid legionella.
Since the upgrade I'm fairly sure it has been necessary to turn up the shower temperature. I had assumed the engineer may have turned down the hot water setting, so I turned it up to the maximum of 65 Deg C using the boiler control. The shower temperature setting still needs to be set higher e.g. 7 out of 10, instead of 5.
It was my understanding that the coil was 16.6w output? (According to Vaillants Website).Spec Sheet:
the unistor260 contains 250 litres of water, it has 22.3kw heating performance at a circulation flow rate of 22.3 LPM (no heating temp given) with a 35 min heating time, primary heating surface 0.75M2.
So presume the controller is looking at the rate of temperature rise and adjusting the boiler flow temp, I think it was mentioned that 75C was noted sometimes?.
It may be of some help to increase the heating output from 16kw to 22kw which may help to get the temperature up within a hour. Possibly some fouling of the heating surfaces as well which won't help.
Spec Sheet:
the unistor260 contains 250 litres of water, it has 22.3kw heating performance at a circulation flow rate of 22.3 LPM (no heating temp given) with a 35 min heating time, primary heating surface 0.75M2.
So presume the controller is looking at the rate of temperature rise and adjusting the boiler flow temp, I think it was mentioned that 75C was noted sometimes?.
It may be of some help to increase the heating output from 16kw to 22kw which may help to get the temperature up within a hour. Possibly some fouling of the heating surfaces as well which won't help.
Don't know what the EN standard is but assuming heating 250 litres from 20C to 65C with 22.3kw, 23.3LPM in 35 minutes gives, by calculation, a deltaT of 8C, rapid heat recovery systems don't care what the deltaT is they use the highest possible boiler temps with the greatest flow rates to achieve their object.
Can't attach files for some reason.
I think you spotted my deliberate mistake SJB.How are you arriving at those figures?
I'm right with you right up until the DT