Baxi boiler works after reset, but shows fault once cool

[mactabby]

Hi - this has baffled me and the heating engineer I've called in to look at it. My Baxi 105e has been reporting a fault, the LED indicating it's with the pump or low pressure. However, a quick reset at the mains and all is well again. If there's either a DHW or CH demand, the boiler fires up and all is well - hot water and rads as normal. BUT - if there isn't a demand, or once the demand has ceased (and the overrun has finished as well in the case of the CH) then the boiler returns to fault mode after about 2 seconds.

The engineer has scratched his head a lot, replaced the PCB (no change) and seems clueless.

Pressure is at about 1.6 bar cold, but over the summer it looks like the boiler was running on low pressure as a result of a leak we hadn't spotted (I've since re-pressurised from filling loop). I'm now wondering whether there could be a problem with the expansion vessel and judging by the dust on the top of the boiler, the engineer hasn't checked it.

Any ideas?

Ta
Mac

 

[Agile]

Yes it is at first sight a difficult problem so I am not surprised he is a little baffled.

Excuse me if I have got it wrong but is there a diverter valve with a pin operating a micro switch at the end? If so is the microswitch actually switching ?? Ot is the pin retracting AND the switch clicking as it retracts?

Next is there a flow switch and when the pump switches off is the pin retracting AND the microswitch actually switching off ??

Tony Glazier

 

[mactabby]

Excuse me if I have got it wrong but is there a diverter valve with a pin operating a micro switch at the end? If so is the microswitch actually switching ?? Ot is the pin retracting AND the switch clicking as it retracts?

Next is there a flow switch and when the pump switches off is the pin retracting AND the microswitch actually switching off ??

Thanks for this. There's a diverter valve and microswitch, and a flow switch, but the boiler has no problems swicthing between DHW and CH while either the burner or the pump is on. I'll check the switches though (as soon as I've had breakfast!).

Cheers
Mac

 

[gstens baxi]

Am I right in thinking the fault occurs when demand is satisfied.

Is your boiler the instant model? because I have never come across the problem you have described.

 

[mactabby]

Hi

Yes - the boiler works perfectly up until the point the demand is satisfied, whether DHW or CH. If CH, it works until the pump overrun is complete. Two seconds later the pump/pressure LED starts to flash and that's that. A reset gets us going again (but only if there's a demand - otherwise it goes into fault mode).

Hope somebody can help with this - the heating engineer is now trying to charge us for changing the PCB even though it's had no effect!

Mac

 

[Agile]

Sorry to all the other RGIs here but I have to say that the engineer who attended should not charge anything until the boiler is fixed.

No fix - No fee is what we work to! As far as the customer is concerned, he wants the boiler fixed and should not be called to pay anything until its fixed.

If a new PCB has not fixed it then the old one should be refitted.

My relevant question about the diverter and flow switches remains unanswered. Some of these problems are caused because of switches sticking or being slow to retract.

I appreciate its a tricky fault but thats not the customers fault!

Tony Glazier

 

[mactabby]

Hi

Thanks for your help. It's fixed now - a problem with the diverter valve. It was sticking for some reason, causing the boiler to think the pressure was wrong. Can't quite work it out, because the boiler is only supposed to switch the valve over when there's a demand from the other side - when the demand is satisfied it's supposed to stay where it is, not reset.

Ah well, at least I wasn't charged for the PCB...

Mac