Strange Prima problem, UPDATED

[ianrp]

Repeat of what I said earlier as its still relevant:-


I dont remember if it will even work with cover off!

You dont say if the pilot lights ???

If not then he should have checked gas valve first stage to see if its powered and if so opening.

If it lights then the flame has not been detected if it keeps on sparking.

Tony

Thanks, Tony.

It will run with the bottom cover off. I'm not trying to start it with the combustion chamber cover off. After fitting the new pcb and calling for heat the relays click and the fan starts (although perhaps quieter than I remember it) but no ignition. If I bypass the pressure switch with a manual switch and switch over after the fan starts running the boiler fires, but then immediately switches off again.

 

[baxpoti]

You dont say if the pilot lights ???

Yes he does

 

[Agile]

It will run with the bottom cover off. I'm not trying to start it with the combustion chamber cover off. After fitting the new pcb and calling for heat the relays click and the fan starts (although perhaps quieter than I remember it) but no ignition. If I bypass the pressure switch with a manual switch and switch over after the fan starts running the boiler fires, but then immediately switches off again.

Yes, but is it the main burner which fires?

That would not happen if the ignition was still sparking!

It has to stop sparking when a pilot flame is detected and then it will power the second stage of the gas valve for the main burner.

Before you were saying it was not lighting the main burner!

"""The pilot lights if pressure is applied to the pressure switch manually or it is bypassed with a changeover switch, but it keeps sparking and the main jets don't light."""

Now which is it?

And has anyone done the tests on the supply to the gas valve and the resistance of the coils?

Tony

 

[ianrp]

Now which is it?

Tony

Sorry Tony, I'm not being clear enough.

Before changing the pcb the boiler would not light by itself but bypassing the pressure valve would trigger the pilot but the sparking would continue and the mains would not light.

After changing the pcb the boiler would not light by itself but bypassing the pressure valve would trigger the main jets, which light and then immediately cut off.

 

[baxpoti]

So changing the PCB has cured one problem?
The burner now lights if the APS is overridden?

It's now down to
a 'tired' fan (you've said it sounds quieter) they normally just fail,
faulty APS or
damaged/incorrectly fitted air tubes.

 

[Agile]

"""After changing the pcb the boiler would not light by itself but bypassing the pressure valve would trigger the main jets, which light and then immediately cut off."""

It seems there is still a problem with no flame detection apart from the fan/aps problem.

One wonders if some of these problems have been added during all the poking about that has gone on.

Tony

 

[baxpoti]

"One wonders if some of these problems have been added during all the poking about that has gone on

Agreed

 

[ianrp]

Thanks guys.

If the fan was running slowly would it create a reason for the burner to cut off quickly?

 

[Trance Nation]

Thanks guys.

If the fan was running slowly would it create a reason for the burner to cut off quickly?

Yes, as combustion products may not be safely discharged otherwise.

 

[Agile]

It would normally take about 15-20 seconds to stifle the burner if the fan was really pulling too slowly on that type of boiler. The flame would obviously be seen to be vitiated!

There must be a very good reason for the flame not being detected!

Has anyone measured the resistance from the flame detection electrode to earth and to the PCB connection ???

All simple tests which any competent boiler engineer would have done!

Tony

 

[ianrp]

Hi guys,

Thanks for the suggestions. Some of these are things I don't want to mess with, so I have another CORGI coming to look at it this evening.

Your help will mean that I can talk sensibly with him and make sure he is looking for the correct problems. I'll let you know how I get on.

 

[ianrp]

Hi guys,

Finally got it diagnosed as a sluggish fan, which responded to proper cleaning and lubrication. Now I just have to decide whether to replace it, strip it down and try to fix it or risk it as it is!

Thanks for all your help.