Pump overrun is killing my heating!

[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?

 

[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.

 

[John.g]

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 also mentions somewhere about switching off the heating pump with no heating demand, maybe this is S.0?

Just saw your post.

 

[milleniumaire]

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.

I just beat you to posting!

The cylinder does have a temperature sensor, which is wired upto the VR 71 wiring centre, so I assume this is being used to get the cylinder to the desired temperature of 65 deg C.

I've been regularly checking the boiler today, since 7:00am and haven't once seen it go into pump overrun. Typical!

 

[John.g]

Re zone temperature control, Presume if a number of zones in service then it should base the boiler SP on the highest heat curve and if only one, on that zones heating curve.

I know you have HW priority and the reason you can't have HW & CH on together is probably the conflicting boiler SP requirements? although one might think that the controller could be configured to select the boiler SP based on the HW requirement or something like this to allow both systems on together.
When HW next selected can you note the actual cylinder temperature, the boiler SP temperature and the actual (thermometer measured) flow&return temps, this will give you a very good feel for what's going on there.

Can you also state the minimum output of your boiler.

 

[EvilDrPorkChop]

What size is the cylinder, 65oc seems a high set point tbh and may explain your reheat issues in the morning.

 

[milleniumaire]

What size is the cylinder, 65oc seems a high set point tbh and may explain your reheat issues in the morning.

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.

 

[EvilDrPorkChop]

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.

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.

This is probably your problem too, getting a 260l cylinder to 65oc, and with the boiler possibly anti cycling because your HW output isn't set correctly then your going to be taking a good 30/45 minutes to get to the set point. Also if you're drawing off in this period it isn't going to help.

 

[John.g]

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.

 

[EvilDrPorkChop]

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.

It was my understanding that the coil was 16.6w output? (According to Vaillants Website).

On HW priority the cylinder will reheat with a flow temp of 80oc.

 

[SJB060685]

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.

But an output of 22kw with a DT of 20°c which my understanding is is what the boiler is looking for is 15.8 lpm. Boiler pumps are burner linked in modern gas boilers?

 

[John.g]

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.