Potterton Prima 80F Fan Cycling on and off

vincentbrown · 6 Oct 2004

Hi, looking for some advice please.

I have a Prima 80F boiler which has the following fault:

1. Call for Heat
2. Small click heard followed by start of Fan
3. Approx 1 second later, larger click heard followed by fan stopping
4. Boiler retrys again after approx 4 to 5 seconds
5. 1 in 5 attempts results in the boiler igniting correctly

I had a similar problem about 4 years ago which was the PCB Control Unit, but on that occasion, the boiler failed to light completely. The fact that it now occasionally lights made me suspect the Pressure Switch, which I have now replaced, but the fault is still present.

Is it possible for the Control Unit to fault intermittently like this? If not, any other likely cause?

I have checked the obvious, such as connectors etc. I have also checked that there is 240V to the common of the Pressure Switch, which there is.

Any advise much appreciated before I spend over £100

on a new PCB.

Many thanks in advance

ChrisR · 6 Oct 2004

Ask me nicely and I'll send you a new pcb for a lot less than that. It does sound familiar, that cycling is what happens when one of the relays' contacts fail I believe.
The powers that be have decided that posting email addresses is "untidy", so you'll have to click on my name in the view where you see all the threads..

But just changing bits is a haphazard way of repairing what is a dangerous boiler. You could have proved the fan pressure switch was OK without removing the cover - which you shouldn't, just by using a voltmeter or even a mains test screwdriver! Which is what I suggest you do now - after all you haven't tested that the fan is producing enough pressure to operate the switch!

Kristoflampie · 6 Oct 2004

Hard to say but in order to progress with the ignition sequence the air pressure switch must be made and stay made so that the boiler knows the fan is running if not it locks out. It could be that it just isnt lighting because of poor ignition spark and the boiler is retrying until by chance a good spark happens and it lights but again as with the fan it should lock out after a set amount of attempts to light.
Difficult fault to diagnose on here , if you are not qualified dont mess with it get a CORGI engineer in.

vincentbrown · 6 Oct 2004

Thanks for the posts.

I have checked the spark gap and it is OK to the specified requirements, but the sequence is stopping just before the spark anyway. When it does light, it does so on the first spark every time.

I have also checked the fan, it is both clean and free.

The sequence of events more accurately is as follows:

1. Call for heat
2. Fan starts
3. Pressure switch activates and 'immediately', fan stops
4. Pressure switch switches back once fan has slowed sufficiently and
'Immediately' Fan is called to start again
5. and so on, unless the fan continues to run after pressure switch activates, when the boiler will light normally.

ChrisR · 6 Oct 2004

Do make sure the aps is electrically changing over. If that's OK it sounds very much like the pcb then - or a connection to it. There really isn't anything much else IN the boiler.

ChrisR · 8 Oct 2004

Was called to Prima yesterday doing exactly what yours is! It was the board. Send me an email & I'll gety one to you tomorrow.

vincentbrown · 8 Oct 2004

Thank you ChrisR, I appreciate your help.

However, I have located a new PCB elsewhere at a good price (e-bay) - If I have problems, or it doesn't turn up, I'll contact you.

Many thanks.

ChrisR · 8 Oct 2004

Could be one of mine then!

vincentbrown · 9 Oct 2004

Whats your user name on ebay?

sailor bill · 30 Dec 2004

I have been having exactly the same symptons as this for a while with the same boiler. The boiler was taking several attempts to ignite but today it has gone dead and silent. There is power going to the fan but it is not turning. There is also live at the brown and white wires of the air pressure switch but not the orange. Pump is also working fine. Is the ignition sequence
1 fan comes on which makes
2 air pressure switch operate and
3 orange wire becomes live which in turn
4 operates gas valve
or have I got the idea totally wrong.
Does the fact that there is power at the fan but it is not turning suggest the fault is with the fan?
Or does it sound as though my pcb is at fault as well as vincents!
Any ideas gratefully received to stop teeth chattering

kevplumb · 30 Dec 2004

power at the fan and its not turning

think you have just answered your own question

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Potterton Prima 80F Fan Cycling on and off

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