Boiler circuit board question

[Bob Smith]

What functions of the boiler are on the two circuit boards of my boiler (Ravenheat RSF82E)? I know one is the control board, and the other is the ignition board.

I have had a long term problem with the boiler stopping in it's light up sequence just before the gas valve comes on, with 2 plumbers unable to decide which component to replace. The gas comes on with a loud "clunk" so I am pretty sure the solenoid is healthy, ie no half hearted / weak operation.

Recently, this has been getting worse. It used to be that the boiler would go for 1/2 an hour until it failed, and since there is no retry, it just sits there blowing cold air through my heat exchanger. Recently, it is getting so it is more often failing than working.

Another thing which has come up in the last couple of weeks is strange on/off behaviour. It has been doing multiple clunks (2-5 times) when lighting up, as well as seemingly ignoring the thermostat knob. There is no click when the knob is turned, but the boiler fires up about once every minute for about 20 seconds. It also fires up at the same rate during the "CH timer off but pump running for a while" state, even though there is no call for hot water. It never used to do this. All this paragraph's problems seem to happen after it has warmed up a bit.

The boiler has never had the 3 minute lock out to stop short cycling.

The only suggestion I got from a plumber (previous to the last 2 weeks new problems) that it may be the sensors on the inlet / outlet failing and confusing the controller. Does this sound familiar to anyone?

Anyway, the main question is, do the above sound like there is a problem with the controller board or the ignition board?

Thanks

Bob

[Ed Sirett]

With this array of symptoms I wouldn't be sure there was one underlying cause other than maybe one of the boards being marginally near failed. However see below.

I've looked through the manual and it appears to be a fairly typical type of combi boiler. I.e. It lights at a low rate and detects the flame using the ignition probe and goes to a higher rate.

However It is possible that for some reason the air flow sensor is on the blink either its inlets are dirty and/or the switch is failing.

As the boiler warms up the density of air through it drops and the pressure due to air flow drops. This gets to the point where the APS is on 'edge' and the chattering is the gas valve dropping in/out/in/out in response to the APS. I'd give a racing certainty that the gas valve relay is more or less directly driven from the APS.

I'd try the following in increasing order of cost and see if you can get a result.

1) Service the boiler. 2) Clean the inlet tubes to the APS. Check and clean the airways and boiler in general if not done under 1. 3) Replace the APS 4) Replace the PCB. 5) Replace the ignition board.

[Bob Smith]

Thanks for that - I have completed steps 1-3, and am contemplating steps

4&5. So far, I have 1 vote for each (if sequence board = ignition board)

Bob

[Ed Sirett]

The mother board is probably the more expensive and the more likely. The flame detection probably has some time delay built in - i.e. 10 seconds with no flame goes to lockout. Ergo the problem is more likely the main board.

[Bob Smith]

It's not the main board. I replaced it today, and all the strange symptoms are still there.

Could it be the solenoid on the gas valve, or the ignition board?

Bob