Pump overrun is killing my heating!

[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?

 

[Murdoch]

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?

 

[John.g]

Yes, re pump overrun but it shouldn't IMO be ever on pump overrun with any demand for CH or HW, I read that the minimum output of this boiler is 12 kw? so if the coil is not absorbing this 12 kw then the boiler will cycle, maybe this is when the pump overrun is showing up. If the coil is absorbing 12 kw then that should heat a 260 litre cylinder from say 25C to 65c in exactly 1 hour, obviously if a 20kw coil, in 36 minutes. If the coil inlet temp is < say 68/70C then the cylinder will never reach setpoint temperature. You can monitor the flow/return temps on the temperature gauges which will tell you something and if you had/have access to a energy monitor you can measure the secondary pump power in watts from which the flow rate can be derived and then you will know exactly what's happening re boiler/coil power.

And presume this is a heat only boiler and not some form of combi!!.

 

[milleniumaire]

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?

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.

By "as well" I mean the hot water heated up and the house warmed up within an hour of everything starting up in the morning.

Yes, I could start the water earlier at 5am and this would probably resolve the issue, but isn't it best to first determine if there is an issue with the way things are working rather than just working around the issue?

 

[John.g]

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.

 

[milleniumaire]

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.

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.

Currently, there is heating demand from all three heating areas (radiators and 2 x UFH zones), as has been the case all morning and the thermostats are showing:

LLH flow from boiler: 58 deg C
LLH return to boiler: 48 deg C
LLH flow to system: 56 deg C
LLH return from system: 46 deg C

I confess, I'm a little surprised the return from the system isn't lower, given it is going through 14 radiators, kitchen/sitting/dining UFH and bathroom UFH!

I have seen the boiler side temps get up to 75 deg C.

 

[John.g]

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.

 

[SJB060685]

With LLH if the system flow is equal to boiler flow then there should be know mixing and an equal temperature maintained, likewise if the system flow was less than boiler flow. If the system flow was greater than boiler flow then there will be a mixed lower temperature going to system circuit/circuits.
The connections in the picture are correct. All a LLH header is an empty tube effectively giving a means of separating two systems with a low pressure loss and low velocity zone. They are also know as a low velocity header.

 

[milleniumaire]

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.

Sorry John, I'm not sure what you mean by setpoint.

On the boiler, the dials are set such that hot water is at its maximum setting of 65 deg C. The radiators are set to 70 deg C. Is this the setpoint?

What is confusing is that the VRC 700 allows the desired hot water temperature to be set more than 65 deg C, but the boiler dial never shows more than this. The VRC 700 hot water setting and boiler hot water setting don't seem to be in sync. Not sure what this is about, possibly an example of where the 10 year old boiler isn't as compatible with the new VRC 700 controller as it could be.

When scrolling through the menus on the VRC 700, there are lots of temperatures mentioned, but the only one's I've changed are the "desired" temperatures, so 21 deg C for the radiator circuit (controlled by VRC 700, which is in the hallway - the coldest part of the house) and 20 deg C for the two UFH circuits.

 

[John.g]

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.

 

[milleniumaire]

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.

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!

This kind of scenario usually ends up with me increasing the heat curve for the zone, making the system less efficient! Of course, the outside temperature also has a large impact and usually, at this time of year, when it is much colder outside, the heating system achieves the desired indoor temperatures more often than not.