Potterton 100 - strange problem

[wadder]

Hi Tony, I'm no heating engineer - just fairly handy with most things mechanical. How do I check the CH sensor?
Last night - went to switch on the CH, started to kettle, vented some water from the prv, then banged a bit and locked out. Left it for 5 mins re-lit the pilot and tried again, as soon as I heard it start to kettle I turned it back to stand by, waited for the kettling to stop then turned it back on again, did this a couple of times, and it eventually worked fine. Seems like it just needs gently warming up to operate properly. Would that point to the wax capsule?

 

[Agile]

The next thing to do is to check the CH NTC ! That should have been the first thing with that symptom.

Its a matter of having and knowing how to use a digital test meter.

Perhaps you need to get someone in?

Tony

 

[wadder]

Got a meter at work, what should the reading be?
Where abouts in London are you based?

 

[HarrogateGas]

The next thing to do is to check the CH NTC ! That should have been the first thing with that symptom.

Its a matter of having and knowing how to use a digital test meter.

Perhaps you need to get someone in?

Tony

Its not the NTC thermistor....the boiler is firing up fine and then over heating BUT the heat is not going anywhere so it will over heat. From the last and more detailed decription of what he said it definatly sounds like the wax capsule operated divertor valve is very slow in opening up and not opening up in time for the boiler to dissepate the heat thus overheating. IF the NTC thermistor was faulty then why is Hot water working percetly fine??

 

[wadder]

Cheers Harrogate - I'll replace the wax capsule and see what happens. I have downloaded the installation and service manual for the Puma 100 from tinternet which contains some good detailed diagrams, here is the link in case anyone needs it for future reference. Thanks you all for your input, I'll keep you posted on my progress!!

http://www.partsarena.com/baxi/System/DATA/Dx/DS1/installation/2245/I04-2245/I04-2245.htm#zFig7

 

[Agile]

Its easier and far cheaper to replace the NTC ! Its so easy to sheck that its the first test.

The boiler can manage itself whatever has happened to the waxstat!

We are based in NW London and cover W, NW and N but never go south of the River as we dont have the Visa! We also go to Watford and the North!

Tony

 

[HarrogateGas]

Its easier and far cheaper to replace the NTC ! Its so easy to sheck that its the first test.

The boiler can manage itself whatever has happened to the waxstat!

We are based in NW London and cover W, NW and N but never go south of the River as we dont have the Visa! We also go to Watford and the North!

Tony

BUT the heat is not going anywhere.....surely if the NTC was faulty and the boiler was getting to hot the complaint would be the radiators get scalding hot and then the boiler goes off......he is saying that the boiler gets too hot but the rads dont heat, how can this be symptoms of a faulty thermistor??


Also the DHW is working perfectly normal, suggesting the NTC is perfectly normal too.

Also in my years of repairing this boiler, the boiler cannot always manage if the wax divertor valve is knackered. Two things on this bouler cause it to oveheat in my opinion, the WAX diverotr or a sticking flow switch.

 

[Agile]

"""Also in my years of repairing this boiler, the boiler cannot always manage if the wax divertor valve is knackered. Two things on this bouler cause it to oveheat in my opinion, the WAX diverotr or a sticking flow switch."""

What do you mean when you say the waxstat is "knackered?

The wax stat fails in the hot water position in my experience and then the system water circulates round the boiler and the CH NTC modulates the burner down and eventually it goes off.

I have never encountered a boiler which could not manage to control itself in that failure mode.

In any case thats exactly what the boiler faces immediately after a DHW demand and it cycles on/off until the waxstat eventually manages to respond which can be anything from about 20 sec when its new to 2-3 minutes when its getting sluggish.

Tony