Pump overrun is killing my heating!

[John.g]

If you use the "orange wire" method as suggested then you must fit relays to the UFH systems to pick up if they are running and also to any zone valve with chopped off orange wires, if too short, one relay might do the wole lotl.
Re your own suggestion above, to prove/disprove it, connect a test light across one of those relays and ensure it stays lit during both normal boiler burner on and off. For pump overrun, observe it while you switch off the last heating circuit, the boiler circ pump should/might overrun and the relay test light should stay on until pump overrun complete.

 

[EvilDrPorkChop]

Can you please confirm how you usually connect it up? Is it the same as my setup:
- Pump is wired into Rel 1 on the VR 40 and d.27 is set to 5

Due to the value of 5, the external pump only works when the burner is on, so it doesn't work in pump overrun, or any other mode where the internal boiler pump is working but the burner is off.

Based on their suggestion to wire it up to the zone valves, I would assume this would cause the pump to work whenever any of the zones are open, which I believe would include pump overrun etc. If not, I wonder what the differences would be.

According to my Vaillant instructions;

d.27 Switching accessory relay 1 in the accessory module 1 = Circulation pump (default) 2 = Ext. pump 3 = Storage charging pump 4 = Flue gas flap/extractor hood 5 = External gas valve 6 = External error message

Why is it set on 5?

In my configurations I would always config to External Pump, so 2.

 

[milleniumaire]

According to my Vaillant instructions;

d.27 Switching accessory relay 1 in the accessory module 1 = Circulation pump (default) 2 = Ext. pump 3 = Storage charging pump 4 = Flue gas flap/extractor hood 5 = External gas valve 6 = External error message

Why is it set on 5?

In my configurations I would always config to External Pump, so 2.

It is set to 5 because Vaillant told my heating engineer to set it to 5! Apparently a value of 5 will cause the pump to run whenever the burner is on. Vaillant seem to be backtracking on the use of the VR 40 and I get the impression they are performing some in-house investigation to try to determine who gave the advice! I assume they record all their telephone calls.

Vaillant told me that if it is set to 2, then the pump will NOT run for hot water demand, which is no good for my system. The pump needs to run for ANY demand, heating or hot water, with DHW taking priority, as all flows (cylinder and heating zones) are from the pump.

I'm sure there are situations that would warrant two external pumps; one for the heating and one for the hot water cylinder, but it would be complete overkill for mine, especially as the cylinder is 1m from the boiler and it is DHW priority, so even if there were 2 pumps fitted, they would only ever work one at a time!

 

[EvilDrPorkChop]

It is set to 5 because Vaillant told my heating engineer to set it to 5! Apparently a value of 5 will cause the pump to run whenever the burner is on. Vaillant seem to be backtracking on the use of the VR 40 and I get the impression they are performing some in-house investigation to try to determine who gave the advice! I assume they record all their telephone calls.

Vaillant told me that if it is set to 2, then the pump will NOT run for hot water demand, which is no good for my system. The pump needs to run for ANY demand, heating or hot water, with DHW taking priority, as all flows (cylinder and heating zones) are from the pump.

I'm sure there are situations that would warrant two external pumps; one for the heating and one for the hot water cylinder, but it would be complete overkill for mine, especially as the cylinder is 1m from the boiler and it is DHW priority, so even if there were 2 pumps fitted, they would only ever work one at a time!

Have you tried setting it to 2 and actually testing it?

In my experience I'm sure it runs whenever there is a Demand.

 

[milleniumaire]

Have you tried setting it to 2 and actually testing it?

In my experience I'm sure it runs whenever there is a Demand.

I haven't, mainly because I assumed Vaillant technical knew what they were talking about when they said:

"Using the VR40 to run the secondary circuit pump run as a heating charge or a DHW cylinder charge Pump not both

Switching of relay 2 on the VR 40 "2 in 7" multi-functional module Options

1 = Circulation pump - DHW secondary Circulation pump

2 = External pump – Heating Charge pump

3 = Cylinder charging pump – DHW Charge Pump

4 = Extractor hood

5 = External solenoid valve

6 = External fault message"

I may just give it a try though if others, like yourself, are setting d.27 to 2 and it works for both heating and DHW.

 

[EvilDrPorkChop]

I haven't, mainly because I assumed Vaillant technical knew what they were talking about when they said:

"Using the VR40 to run the secondary circuit pump run as a heating charge or a DHW cylinder charge Pump not both

Switching of relay 2 on the VR 40 "2 in 7" multi-functional module Options

1 = Circulation pump - DHW secondary Circulation pump

2 = External pump – Heating Charge pump

3 = Cylinder charging pump – DHW Charge Pump

4 = Extractor hood

5 = External solenoid valve

6 = External fault message"

I may just give it a try though if others, like yourself, are setting d.27 to 2 and it works for both heating and DHW.

According to the instructions of the actual boiler, it states 1 as Circulation Pump, and 2 as External Pump. In my experience in fitting them, the boiler states this too when configing them up. Don't trust Vaillant technical, they hardly know out about their own boilers never mind wiring them

Try 2, there's no harm done. You can just change it back

 

[milleniumaire]

According to the instructions of the actual boiler, it states 1 as Circulation Pump, and 2 as External Pump. In my experience in fitting them, the boiler states this too when configing them up. Don't trust Vaillant technical, they hardly know out about their own boilers never mind wiring them

Try 2, there's no harm done. You can just change it back

So, I set d.27 to 2 this morning.

The system was in heat mode and the pump was on. This continued. I then turned up the temp of the water from 55 to 65 and it immediate switched to DHW mode. The external pump continued to run. It took around 15-20 mins to heat up to 65, then switched back to heat mode. I didn't see any pump overrunning so while this setting is obviously working for hot water as well as heating (contrary to what Vaillant suggested), I'm currently not sure if there are any situations when the external pump will run now, when it didn't before i.e. is there any difference between a setting of 2 or 5 in terms of when the pump runs.

I'll keep an eye on it throughout the day.

I'm assuming just changing the setting is enough? The boiler doesn't need to be reset to accept the new setting by power cycling it or anything?

 

[John.g]

D.27 5 is IMO only designed as a safety device, ie shuts a outside gas isolation valve when the burner shuts down or something similar, that's why the ext pump was only running with the burner on. D.27 2 works exactly as one would (now) expect, it runs a additional circ pump, period.
If you wish to check for pump overrun just decrease the wall stat setting (if on CH) until the boiler shuts down, it should then do a pump overrun, also check if it keeps the zone valve opened otherwise you may have to consider installing a ABV or a normally open mot valve in the secondary circuit.

 

[milleniumaire]

D.27 5 is IMO only designed as a safety device, ie shuts a outside gas isolation valve when the burner shuts down or something similar, that's why the ext pump was only running with the burner on. D.27 2 works exactly as one would (now) expect, it runs a additional circ pump, period.
If you wish to check for pump overrun just decrease the wall stat setting (if on CH) until the boiler shuts down, it should then do a pump overrun.

Thanks for the info on how to force pump overrun, you were spot on. As soon as I turned the temperature down for each of the heating zones, the boiler showed S.7 - pump overrun and the external system pump continued to run. Result!!!!

I think that just about solves all my issues and the external pump seems to be working at the same time as the internal boiler pump.

My heating engineer is visiting on the 25th to service the boiler so I'll have a chat with him to confirm who decided on setting d.27 to 5. I've always assumed it was as a result of advice from Vaillant as I know he was on the phone to them 2 or 3 times during the upgrade and specifically for info on wiring up the new pump. So maybe the advice to use the VR 40 was correct and the current advice to instead wire up the pump to the VR 41 is tosh! I'll play it out with Vaillant technical support and see where it goes as it appears they still think using the VR 40 was the wrong thing to do!

 

[John.g]

Might also be worth also checking if it keeps the zone valve opened for the overrun period (otherwise despite what I thought previously) the ext pump will have no pathway for the water, (with/if all zone valves closed), it may not do the ext pump any harm if the overrun is only for a minute or so.