Which component fails on Potterton 80E control board?

[feynman]

My Potterton 80E has just failed. It has the clicking air pressure switch and the fan runs and cuts out - runs and cuts out etc. The flue is clear and not rotted out - the air pressure switch moves and the switch contacts change electrically, but the control board does not start the ignition sequence.

There are volts at the PCB and the fuse on the PCB is good. I have re soldered all the connections on the PCB in case of dry joints, but to no avail.

Does anyone know which component(s) fails? It is a simple circuit with 2 relays, 3 transistors and a handful of diodes. I am about to start tracing the components and working out the circuit diagram, but if anyone can give suggestions it might save me a lot of time.

Bloody freezing in the house, so it would be great if I can sort this today. (I know you can still buy new boards, but if just a transistor or a relay has gone, it might be an easy and quicker fix).

Thanks in advance.

 

[gazfen]

Ask a gas safe man.

 

[gazfen]

Ask a gas safe man

 

[feynman]

I heard you the first time.

We are talking simple electronics here, not gas. A gas man would just change the whole board, they wouldn't fault-find to component level and change the failed component. So. Do you know which component(s) tend to fail on the board?

I removed both the relays from the board, activated them with a bench PSU and they both work. However, one has more than zero resistance from its common terminal to its NC terminal. I swapped the relays over so that the one with the high resistance is in the slot where that terminal is not used by the circuit.

Additionally, I have discovered that in the clear air-tube there is a brass restrictor. This seems to have been blocked, so I cleared it out with cleaner spray. Now, the boiler fan will run constantly - whereas before, it would only run for 10s then turn off and cycle on and off. So we are making progress.

I have also found that the pilot light gas valve does work - by plugging the gas solenoid into the test socket on the front.

So the problem that remains is that the ignition and the gas solenoids are not operating, even though the fans now runs constantly. What might be preventing them doing so?

Any ideas?

 

[RandomGrinch]

We are talking simple electronics here, not gas. A gas man would just change the whole board

Whether we like it or not, I'm afraid the forum rules disagree with you here:

DIY GAS

IS DIY GAS LEGAL? Diy gas work is not illegal, BUT, the law does require that only competent people may work on gas appliances. You also have to be able to test anything you've done, so you need the right equipment and have the right qualification to use it. The Gas Safety Regs 1998 states...

www.diynot.com

 

[Mottie]

We used to have a Potterton Profile 60E and I changed my circuit board three times during our 25 year ownership. Pretty sure I just lowered it down from underneath and replaced it. My memory may be playing tricks but I don’t remember unsealing anything to get to it. If so, is that not allowed unless done by a gas safe registered person?


NOT allowed under the gas Regulations
You are not "competent" to test the boiler afterwards.

 

[RandomGrinch]

If so, is that not allowed unless done by a gas safe registered person?

Whether it is or isn't, talking about swapping out PCB's on the forum, would probably come under these rules.
As it is, the OP is talking about the board at a component level. That has a different level of risk.
And this is an open forum; if we suggested a component change that someone else, far less competent than the OP copied in the future, the outcome may not be a good one.

 

[feynman]

OK but in that case, it begs the question why have a central heating forum at all.

I am an engineer of about 40 years, specialising in electronics.

Just needing to fix a simple circuit board.

I understand gas safety concerns; and the corporation where I was originallly trained for three gears in electronics was, and is, very strong on health and safety and risk assessment. My subsequent careers have been similarly strong on safety and risk avoidance.

If you said to me that your car, (for example), was misbehaving - and I said you could clean or replace the MAP or MAF sensor, or change the alternator, yourself, (depending on the symptoms), would you say "no I will book the car into the garage and pay for them to fix it." Or might you do it yoursrlf - assuming you had the requisite competence?

NOT allowed under the gas Regulations
You are not "legally competent" to test the boiler afterwards.
Unqualified uninformed interference with circuit boards in boilers is barred by the manufacturer, the Regulations, your insurance company, and this forum.