Pump overrun constantly on

[lulusi]

Hi all, I know there’s a million posts on this topic but I can’t find the answer..

I have an Vailant EcoTec plus 438. It’s on an S-plan system (2x valves in airing cupboard next to cylinder) with a new wet UFH system added for the kitchen, seemingly on its own zone/system (separate thermostat/timer pump, wiring centre, etc).

Everything works fine (CH for rest of the house, HW, and UFH) except the circulating pump in the wiring cupboard before the 2x motorised valves is permanently running, even when the CH+HW and the UFH is off.

I checked the wiring in the wiring centre in the airing cupboard, nothing obviously wired incorrectly, and the valves and the cylinder thermostat are working correctly.

It just seems that the boiler is constantly running the pump. The pump overflow symbol (like a sand timer) is not displayed longer than 5 minutes after CH or HW programs are on. However, the tap icon is solidly illuminated all the time. The manual says this indicates “heating of an indirect hot water cylinder turned on”… is this normal?

I can’t for the life of me work out why the pump is running all the time. Might something be wrong with the boiler? Or is there something about how the UFH circuit was added which might have caused the circulating pump upstairs (but not the UFH pump) to run constantly, either by design or by accident?

Any suggestions gratefully received. Thankyou.

 

[lulusi]

I read in various places that some earlier Grundfos UPS2 pumps were causing surges that fried the boiler overrun control circuits. The pump was replaced in 2018 (before I moved here, but after the UFH was added) … could it be that it had already fried the boiler circuit, and then wore itself out… the old owners replaced the pump but not the boiler PCB and hence the new(ish) pump is running constantly if the relay is fused?

 

[old duffer]

I read in various places that some earlier Grundfos UPS2 pumps were causing surges that fried the boiler overrun control circuits. The pump was replaced in 2018 (before I moved here, but after the UFH was added) … could it be that it had already fried the boiler circuit, and then wore itself out… the old owners replaced the pump but not the boiler PCB and hence the new(ish) pump is running constantly if the relay is fused?

The siren call of the industry..."replace the PCB" lol.

 

[Gasguru]

When the original UPS2 pumps were powered on they drew an excessive current (inrush) and the relay contacts on many boiler pcbs and controls were fried (and potentially welded on).
If you have a multimeter you could check the status of the pump feed at the boiler with no demand to the boiler and after a pump overrun time has expired.

 

[old duffer]

When the original UPS2 pumps were powered on they drew an excessive current (inrush) and the relay contacts on many boiler pcbs and controls were fried (and potentially welded on).
If you have a multimeter you could check the status of the pump feed at the boiler with no demand to the boiler and after a pump overrun time has expired.

and you are a gas guru! wow...this is why the industry is in such a state

 

[lulusi]

so it seems as if there is nothing wired into the boiler’s pump terminals. which I guess is no surprise why it is running all the time. would it damage the boiler if I wired the pump across the valve switched live for the valves? i.e. so that the pump only activates when one or both of the valves are open? this would mean no overrun at all, compared to now where there is a permanent overrun because it appears the pump has not been wired into the boilers pump output terminals (they are empty)

 

[old duffer]

so it seems as if there is nothing wired into the boiler’s pump terminals. which I guess is no surprise why it is running all the time. would it damage the boiler if I wired the pump across the valve switched live for the valves? i.e. so that the pump only activates when one or both of the valves are open? this would mean no overrun at all, compared to now where there is a permanent overrun because it appears the pump has not been wired into the boilers pump output terminals (they are empty)

That would be a very effective and quick fix. How come the gas engineers have not mentioned that route?

 

[ianmcd]

because it appears the pump has not been wired into the boilers pump output terminals (they are empty)

where is the pump wired into then ?

 

[stem]

I was once asked to look at the same problem where the pump ran permanently and the boiler's pump output terminals were empty. Turns out a new boiler had been installed that required a pump overrun [the one it was replacing didn't] Without the pump 'overrun' the new boiler 'overheat' would trip at the end of the heating cycle.

The installer was called back to rectify the overheat problem and it appears that the lazy chap, instead of running a new cable down from the pump in the airing cupboard to the pump terminals at the boiler in the kitchen, instead connected the pump to the convenient permanent live of the motorised valve (i.e. grey wire) so it stopped the 'overheat' trip but the pump ran all the time 24/7.

Not saying that this is the case with yours but the symptoms and the empty terminals are the same....

So, I suppose it comes down to as per @ianmcd

where is the pump wired into then ?

 

[ianmcd]

I was once asked to look at the same problem where the pump ran permanently and the boiler's pump output terminals were empty. Turns out a new boiler had been installed that required a pump overrun [the one it was replacing didn't] Without the pump 'overrun' the new boiler 'overheat' would trip at the end of the heating cycle.

The installer was called back to rectify the overheat problem and it appears that the lazy chap, instead of running a new cable down from the pump in the airing cupboard to the pump terminals at the boiler in the kitchen, instead connected the pump to the convenient permanent live of the motorised valve (i.e. grey wire) so it stopped the 'overheat' trip but the pump ran all the time 24/7.

Not saying that this is the case with yours but the symptoms and the empty terminals are the same....

So, I suppose it comes down to as per @ianmcd

That was my exact thinking @stem