Potterton Prima-F reigniting

[Al]

Pretty sure I posted on this last year, but a similar problem has come back :(

Potterton Prima-F fires up happily on demand, but sometimes, after 5 seconds kills it's gas supply and reignites. This can happen several times,

5 seconds between each occurance. Doesn't always do it.

Last time I was convinced that the thermocouple or control board had an intermittant fault, but our usual plumber/gas bloke pointed out that the flame was lifting from the burner, was a bit orange, and that the inner cylinder of the flue was totally corroded. He was right - Inner annulus was like a net curtain and leaking exhaust gasses back into the air intake. Replaced (remarkably expensive for a metal tube) and the problem went away.

Now the problem has come back. This time the burner looks good, bright blue flame, not lifting, but every few/five seconds cuts out and reignites. It is sadly intermittant, so whoever I get to look at is likely to waste a lot of time waiting for the fault.

My guess is the control board (It failed a few years ago and was replaced).

Any other thoughts?

Al.

[geoff]

In message , Al writes

possibly, but not a common pcb problem

I do a recon one for £30 ++

probably the cheapest way to find out

[Vortex2]

I have this boiler and had this problem a couple of years ago.

As I recall there is a horizontal PCB bottom, left towards the back with a 4 pin "header" connector carrying mains supply and boiler control line. I found a dry joint where this was soldered to the PCB

I suggest you remove and check this PCB, resolder thes ejoints and see if the problem goes away.

D

[Ed Sirett]

Most likely a failure of flame sensing. Check ignition lead HT can still work thru a poor connection but but flame sensing. Maybe PCB.

Estimate boiler at about 14-20 years so maybe look to a replacement soon? Especially seeing as it has a serious flue fault.

[Big Les Wade]

Al posted

I had exactly the same problem with a Potterton Kingfisher this winter. The cutting out and reigniting was accompanied by an awful lot of clicking of relays. I replaced the main PCB, which fixed it completely.

But going another step further, what caused my PCB to fail (it was only

3 years old)? I have been advised that it may have been excessive cycling. That, in turn, would have been caused by inadequate water flow through the heat exchanger. Which points either to furred-up pipes, or a tired (or under-specced) circulator pump, or both. When the summer comes I'm going to replace the pump and see what that does.

[geoff]

In message , Big Les Wade writes

You used the word "potterton" and then missed the obvious reason

[Al]

Still not got around to investigating further. Occurances are really random :-(

I noticed some years ago that the HW cylinder stat was set too close to the boiler stat. As a result the heat losses from the pipework were causing the boiler to be fired every few minutes. Set the HW stat to something sensible and set the boiler stat 10 degrees higher. Sorted.

I checked that the pump overrun was working, so there shouldn't be a problem. No evidence of furring, and the pump seems to do a good job.

I'll wait until the weather is a little warmer and check for dry joints (as suggested) and possibly try recon PCB(s).

Al.