CH boiler air pressure switch

[FrederickDeLarge]

Hi Everyone,

As a newcomer to this forum I have been reading with interest other folks' CH problems and am impressed at the enthusiastic help so willingly offered by experts. If I can possibly do the same on any topic, I will gladly do so.

My own present question is what to do about a boiler that has difficulty in firing up. The initial fan blower process starts up OK but cuts out after a few seconds, to immediately activate again for another few seconds, cut out again, restart, cut out and so on. This hiccup cycle runs for 25 times or so before the familiar clicking of the spark process is heard and the boiler starts up as normal. I suspect the air pressure switch is failing. Could there be anything else at fault? Would be grateful for any help.

 

[picasso]

make and model of your boiler would be a good starting point.

 

[FrederickDeLarge]

Thanks for the reply - the model of boiler is a Potterton Netaheat Profile 60e.
Just over 20 years old so not very young but, until this problem occurred everything was working effortlessly.

 

[picasso]

The fan cycling on and off is normally a sign of the control board being faulty.

 

[gasafengineer]

As said usually faulty board (relay)......................other issues with these boilers are pilot light letting-by which will cause the fan to ''hunt' , check whether pilot light remains on when no call for heat (gas valve faulty) , other issues are hole in inner flue , air switch....................other problems unrelated to your issue are air pressure hoses collapsed @ back of switch (springs left out) or mre commonly air proving restrictor blocked.

 

[FrederickDeLarge]

Many thanks. Is the evidence strong enough in your view to risk going to the cost of a replacement control board?

 

[nickso]

yes, extremely common fault. 90% probability of it being the pcb.

 

[gasafengineer]

Many thanks. Is the evidence strong enough in your view to risk going to the cost of a replacement control board?

NO , check above postings first , i'd like a pound for every board fitted to these boilers that wasn't necessary.

 

[FrederickDeLarge]

Hi gasafengineer - many thanks for the suggestion about the PCB. Not quite the solution I wanted to hear for if that component is suspect, checking by substitution (at app. £135) is a bit of an expensive play! I don't think the other symptoms you mention are showing - the pilot does extinguish as required and the fan unit, replaced a few years ago, runs without problem.

On that subject I have an old Potterton spare PCB unit and on inspection I can't see anything that wouldn't be familiar to a competent radio engineer - a couple of relays, a double wound coil (HT presumably), two small diodes, a rectifier, various capacitors and resistors. There are also three unidentified transistors, unidentified so that they might not be so easily replaced? Thus new replacement PCB units might be the easier option to mending 'failed' ones which might otherwise have the chance to get up and running again for a couple of quid!

 

[ChrisR]

Yes, they're low tech boards with low tech faults, well known to boiler menders who also happen to have electroniics knowledge.
Potterton and the others probably make a lot more money from overpriced spares than selling boilers in the first place.

I must have replaced 3 - 4 hundred of those boards, after some simple diagnostic checks, and only once it was something else!

You have to be Gas Safe Registered to change the board and test the boiler afterwards.

 

[Agile]

And for that matter to touch any of the other components mentioned above which is probably contrary to the site rules!

 

[ChrisR]

Come to think of it it's a Positive Case Pressure boiler, which makes it a killer if you don't do the right checks, so NEVER take the cover off. I'm not joking, people died so they redesigned the next model.

 

[gasafengineer]

Hi gasafengineer - many thanks for the suggestion about the PCB. Not quite the solution I wanted to hear for if that component is suspect, checking by substitution (at app. £135) is a bit of an expensive play! I don't think the other symptoms you mention are showing - the pilot does extinguish as required and the fan unit, replaced a few years ago, runs without problem.

!

Hole in flue is a common fault with these boilers as is pilot letting -by , would say 8 out of 10 faults on these boilers are board related , a simple check as posted above can save some £££££s when purchasing a PCB that won't solve the issue........................'normally' a slight tap on underside of control panel will kick the burner into life as will dropping control panel down , a VERY simple boiler to diagnose , so simple in fact some engineers change boards as par for the course then tell customer another component has failed when boiler fails to fire.

 

[mysteryman]

Bear in mind also that the pcb contains all the flame failure safety systems. I would check everything else before spending on a new board.

 

[FrederickDeLarge]

Thanks everyone for your great advice. The caveat 'don't do it yourself' is a sound one - the wrong mixture of gas and air will give you a highly explosive bomb. My brother is gas safe registered and it is he that I was going to get to 'help out'. My concern was to obtain any parts first so as to minimise trouble for him. I haven't even told him of this current problem - yet. I owe him enough already.