Potterton Lynx electronic boiler fault

[michael194]

Hi all, first post.

Firstly, let me explain that I am an electronics engineer and my trade is with the TV & hi fi repair industry.

I have a Potterton Lynx electronic with a rather peculiar fault.

When the boiler comes on first time it comes on OK and central heating works. However when it needs to reignite for instance when hot water is switched on, or after using hot water, the demand light and ignition light will come on it will try igniting but wont, the ignition light will go out leaving the demand light showing and the fan running.

If you switch the boiler off for say 10 seconds, it will start up and run until it needs to reignite itself. I sometimes have to do this several times.

It isn't the electronic large board, the one with transformer, the capacitors were replaced by me a couple of years ago.

The Full sequence control board was replaced a few months ago when the boiler wouldn't fire up at all.

All dry joints on both this and the other boards have been attended to.


Additional info:

When the fault occurs, you can see the ignition sparking for a couple of seconds, sometimes the gas ignites for a few seconds then goes out. When the boiler works normally the ignition sparks for say 5 - 10 seconds.

Having observed more about what is happening, I'm wondering if the problem is caused when the heating has reached temperature and the boiler tries to switch from high flame to low flame.

I know this boiler is old, but when it works it works well and I dont have the money to replace it.

Thank you for you time and help.

 

[diamondgas]

Sounds like an ignition issue for sure You'll need a GSR engineer to check out the gas valve and pressures supplied by it ... It sounds like you know your way around the boiler so you could check that the spark gaps correct and if it has a separate flame sensor, that that gap is correct too. If you;re not confident in doing that though leave it to the expert

 

[RoryD]

As per Diamondgas, however, to anyone who will listen, the neutral o the pcb (top left) is prone to loose joint and arcing. Quite a few still around on our "patch".
Merry Xmas to all

 

[michael194]

Thank you to Diamond gas and Rory I will speak to my engineer and see what he says.

Rory, I've gone over all the dry joints, if the neutral was arcing, you wouldn't get any LED's lighting.

What are the chances that the gas valve is faulty?

Merry Xmas Michael

 

[diamondgas]

There's a chance the pressers have faltered so are bordering on the appliances limits of detection on ignition and therefore every now and again detecting an anomaly! However without checking out against the mi's you wouldn't know!

 

[michael194]

Well the gas valve was bought and fitted but failed to rectify the fault. whilst it was out, we vacuumed out the heat exchanger and checked the ignition and sensors but both appeared OK.

So what could be next?

The only thing I can think of is the modulation PCB, this has never been changed. I could easily check/replace the capacitors, if its the original, they may well be starting to show their age.

Otherwise its a new boiler.

 

[RoryD]

I suspect that this must happen for the heating too. s trying to fire but the gas ain't gettin to see if there is a pressure there.You need to check the gas valve resistances or electrodes. It does sound like it lights and then cuts out (not rectifying). Engineer should see if he gets correct pressure on ignition.

 

[michael194]

It does happen on heating, it doesn't cut out on hot water, but it wont fire up on hot water if it has 'tripped out'