Potterton Performa 28 - Intermittent heating problem

[Gaz79]

Hi I don't know if anyone can shed any light. After taking apart DHW valve to troubleshoot earlier problem the heating is now struggling to come on.
With heating switch turned on the boiler starts up, the pilot light starts, the heating comes on then the flame goes out, it then struggles to relight a few times before giving up leaving the normal noise of the boiler and no hot water pumping through to the radiators.
The hot water is unaffected.

It then works when tried later on but then same problem when turned on again.

I sprayed WD40 on the push rods in the DHW valve as it was sticking and when trying to free the mechanism may have slightly bent the push rod attached to the plastic disc.
Would this cause the heating to struggle coming on?
Or could it be an air lock?

Back story: I've had an earlier problem with the heating coming on every time the hot water's run so i replaced the one diaphragm in the diverter valve, that didn't work so just bought a replacement for the 3 way valve so hoping that will fix that problem.

Any help much appreciated.

Thanks,
Gareth

 

[Agile]

Boilers don't struggle and that model does not have a pilot light.

It does sound as if the manifold section of the diverter is sticking and not following the hydraulic actuator.

Replacing the whole unit should solve the problem. They can be a little tricky to change though.

Tony

 

[Gaz79]

Thanks for your help again Tony.

Think i must mean the flame for the burner.

Is it possible to fix or just buy a part for the manifold? As it's quite pricey and i'm a bit strapped.

Thanks

 

[Agile]

Some say they can be dismantled and cleaned.

I once spent quite a while cleaning one by boiling in citric acid and doing the work on the patio with a friend's very pretty girlfriend.

In spite of taking so long on it the valve only worked for a couple of months and then I fitted a new one and that has been fine for the last three years!

Tony

 

[Gaz79]

Thanks for your help Tony. Do you think replacing this will also fix my earlier problem of the heating coming on when hot water's on?
Thanks

 

[Agile]

earlier problem could well be caused by the same seized manifold section. But this would be visible because the pin would be stuck out and operating the switch with no DHW demand.

It is also caused by a tight pin gland on the hydraulic unit.

It can also happen WITHOUT the pin extended if the switch is failed which is a very common fault..

Tony

 

[Gaz79]

Brilliant! I'll have a good look at it now you've pointed me in the right direction.
Thanks for your help Tony!

 

[gas112]

So when it lights how long is it staying on for seconds or ?

 

[Gaz79]

At the moment it seems to be working ok (touch wood).
But when it's got the problem the flame lights for a few seconds and stops, this repeats for a while until it gives up. Then trying it later on it works until the hot water is used then won't come back on but like i said last night and this morning seemed to work ok.

I'm wondering whether it could be an air lock after i drained the system? As i was running the boiler with the 15mm Cold Water Inlet switched off!

 

[Agile]

If its not staying on reliably once lit then you could check the pump proving switch on top of diverter valve is being reliably activated.

Best checked by measuring the voltage across it.

Tony

 

[Gaz79]

Right i'll have to get my hands on a voltmeter. What should the reading be? Cheers