Potterton PROMAX Combi HE Plus - FAN/PUMP running when IDLE

[red.barchetta]

Dear Community,
My very elderly parents have a Potterton Promax Combi HE Plus boiler. It is under breakdown maintenance with British Gas to which each fault claim attract an excess fee.

With that assurance of breakdown in mind, we have been having an ongoing issue with the boiler, one which BG seem not to be able to fix.
The issue - when using HW is finished, and there is no further demand for HW, the fan/pump should switch off. It doesn't for period of 15-mins, 30-mins, 1hr. There is no fixed pattern.

When BG came they have never heard of this issue before and changed divertor valve and motor which sits on top of divertor value. Since then I have been monitoring, and the problem is still there.

Sometimes, at 2am in the morning, when no in the property would be using HW, the boiler fan/pump is still running.

The temp gauge on front can read 86-87 degrees and the TAP LED is ON.

I am at a loss why this is happening and for fan/pump to keep running suggests there is still an underlying fault. It cannot be right that fan/pump doesn't switch off after 5-mins or less of last call for heat.

Because it is at my elderly parents home, they would not know what the boiler is doing.

In light of the issue still being apparent, I am going to get BG back in again on the basis of original fault still existing.

Reason of posting it here, would be to see if any expert in this community could suggest what I can tell BG to check when they come back. I know, they should be telling what the issue is, and fix it, but right now that is the concern.

Any help would greatly be welcomed.

Thank you sincerely,

Red.

 

[CountryFan]

Sounds like it could be a stuck/sticking flow sensor. Remove the cover and towards the right of the gas valve there should be a Hall effect sensor, if this is lit red next time it faults then this is likely your issue.

 

[red.barchetta]

Dear Stuckinarut,

You are definitely onto something.
See picture below. When idle the pump is so hot to touch as is divertor valve and fan & pump both on. Nothing is calling for HW.
This has been going on since April. Will let you know here of the outcome.
Thank you sincerely.

 

[CountryFan]

Dear Stuckinarut,

You are definitely onto something.
See picture below. When idle the pump is so hot to touch as is divertor valve and fan & pump both on. Nothing is calling for HW.
This has been going on since April. Will let you know here of the outcome.
Thank you sincerely.
View attachment 386812

Yep, so if nothing was running when you took that photo, it’s lit red (as I mentioned), so stuck hot water sensor. Iirc, you should be able to get just the cartridge replaced. If hot water isn’t needed all that much, you could remove the Hall affect sensor (clear plastic bit on top) and then it should stop the pump/fan etc running.

As an aside, that automatic air vent looks like it’s leaked previously or still leaking

 

[red.barchetta]

Thanks again for your input and comments. It *really* is appreciated.

Yes, when cartridge is removed, led goes off, and fan & pump stop. If put back on again, clicks-in, red light comes on and hence pump and fan. All this happens when there is no demand for HW.

I agree changing the cartridge, but not sure what it sits on top of and whether it is also faulty too? I will let BG look at it when they come in on a repeat visit for the same fault.

Honestly, sitting idle with pump & fan running has been there for a very long time, my parents put it down to "boiler is doing something".....

I also take note of your comment about air-vent. Yeah, it looks not quite right, but there is no visible leak, I will mention it to BG too.

A question from me please. Why would the pump and surrounding pipes be so hot to touch, especially when the burner is off when idling? As mentioned before it can sit there like that till 2am when no one is using HW or CH. Is something heating it and has there money been wasted by it not cutting out when it should do?

Thank you again sir.

 

[CountryFan]

You’re very welcome. To answer your question - it will likely be heating up as it thinks there is a demand - a hot tap running. You didn’t remove the cartridge - you removed the Hall effect sensor, the cartridge is the brass part but has the magnetic flow sensor part, sometimes screwed in, and therefore replaceable.

The way it works is the bobbin (magnetic part) spins when the hot water is being ran, this magnet has become stuck and therefore reacting with the Hall effect sensor (clear plastic thing you removed), hence why it’s lit red. This can be removed until repaired, however it will leave them without hot water.

 

[red.barchetta]

You’re very welcome. To answer your question - it will likely be heating up as it thinks there is a demand - a hot tap running. You didn’t remove the cartridge - you removed the Hall effect sensor, the cartridge is the brass part but has the magnetic flow sensor part, sometimes screwed in, and therefore replaceable.

The way it works is the bobbin (magnetic part) spins when the hot water is being ran, this magnet has become stuck and therefore reacting with the Hall effect sensor (clear plastic thing you removed), hence why it’s lit red. This can be removed until repaired, however it will leave them without hot water.

Thank you so much. And also correcting me with difference between Hall Sensor & Cartridge.....

Can I ask, what is heating it up the pipes and pump. Just residual water in it after last call for HW? When idling like that, it can stay for hours and hours and pipes just as hot (2am in the morning). Always in that mode the front panel display shows:-
the tap led is on,
the rad led off
burner led off

 

[dilalio]

Are you sure boiler is not firing?
If there's a call for heat (falsely in this case) the boiler will try and fire and build heat very quickly as nowhere for it to go. This is what is giving you the temp readings you mentioned, is it not?

The temp gauge on front can read 86-87 degrees and the TAP LED is ON.

Also, pump will generate heat.

You defo don't have any hot taps dribbling do you?
Isolate cold feed to boiler and see if led stays lit on flow sensor.

 

[gas112]

The burner will be firing for very short periods with this fault. That is were the heat is coming from.

 

[red.barchetta]

Are you sure boiler is not firing?
If there's a call for heat (falsely in this case) the boiler will try and fire and build heat very quickly as nowhere for it to go. This is what is giving you the temp readings you mentioned, is it not?



Also, pump will generate heat.

You defo don't have any hot taps dribbling do you?
Isolate cold feed to boiler and see if led stays lit on flow sensor.

Hello Dilalio,

I can confirm 100% no dribbling of hot water - at least nothing coming from any taps and further no leaks from boiler. It was the 1st thing I checked and also considered.

Perhaps as you say, falsely demand for HW is there and burner turns on briefly and off again, but the pump & fan keeps going.

The most annoying and intermittent thing about the issue is, that sometimes it behaves, meaning when no demand for HW, the pump and fan are off. And equally when there is demand, it would serve, and then switch off again after 2-3mins. The correct behavior.

Then randomly in the day/night, when there is demand for HW, it will serve, but this time, keep idling (pump & fan on), sometimes hours! This is the issue and is not right, suggesting an underlying problem.

As mentioned, sometimes it can be idling at 2am in the morning, when I know no one is using HW. Hence when last demand was served, it never switched off.

Thank you for your input.

 

[red.barchetta]

The burner will be firing for very short periods with this fault. That is were the heat is coming from.

OK, understood and makes sense.
Thank you.

 

[gas112]

basically its a magnetic switch as you turn the hot tap on and water flows a little bobbin rises up inside the brass bit activating the sensor (red light) to bring the burner on
when the tap turns off it drops back down deactivating the sensor turning the gas off . Quite a common problem the bobbin is sticking up and not falling back down so boiler thinks there is a HW demand .
. Your brass bit doesnt look like it has any weepage around it so hopefully it should come out ok but they sometimes collapse and it then needs the entire brass block it screws into

 

[red.barchetta]

Hello everyone.

Just to give you an update. The engineer who came today saw and said immediately it was "flow sensor". He replaced it, and it now works a treat .

I was well armed with all the facts given by you (Stuckinarut).

All day I have been opening/closing H/W kitchen sink tap and boiler kicks in, serves, and afterwards stops (including pump & fan). In the past it would be on for 3-4 hours with parents not realising anything was wrong.

Take care & thank you.