I have a potterton suprima 60 boiler which over the last 2 weeks has
gradually got worse with the locking out problem. I've had the PCB out
, fan, air pressure switch ( which i have tested for continuity)
cleaned all contacts. Everytime I have a look at the innards of the
boiler( 3-4 times so far) it works perfectly for 24-36 hours before
starting to lock out more and more frequently until it goes straight
to lock out after a few attempts at lighting. At the moment the boiler
ignites and burns for a few seconds but the the green light continues
to flash at high frequency instead of going on continuously as it
should , the burner then extinguishes. According to the fault finder
flow chart the problem is either with the PCB or the gas valve,
depending on whether there is 300vDC between red and black wires to
the gas valve. I need to get a volt meter to check this. The PCB is a
reconditioned unit from CETltd which I purchased last Winter after
similar lock out problems although last years problems were sorted out
with a new air pressure switch. When I took the PCB out I noticed some
scorch marks around some of the resisters on the middle of the board.
My gut instinct is to replace the PCB again as this seems to be the
common fault with these boilers. It seems like the control is not
getting a boiler has lit signal and so switches off the gas valve. Any
suggestions gratefully received.

Jim

"Jim Thorogood" wrote in message
...
I have a potterton suprima 60 boiler which over the last 2 weeks has
gradually got worse with the locking out problem. I've had the PCB out
, fan, air pressure switch ( which i have tested for continuity)
cleaned all contacts. Everytime I have a look at the innards of the
boiler( 3-4 times so far) it works perfectly for 24-36 hours before
starting to lock out more and more frequently until it goes straight
to lock out after a few attempts at lighting. At the moment the boiler
ignites and burns for a few seconds but the the green light continues
to flash at high frequency instead of going on continuously as it
should , the burner then extinguishes. According to the fault finder
flow chart the problem is either with the PCB or the gas valve,
depending on whether there is 300vDC between red and black wires to
the gas valve. I need to get a volt meter to check this. The PCB is a
reconditioned unit from CETltd which I purchased last Winter after
similar lock out problems although last years problems were sorted out
with a new air pressure switch. When I took the PCB out I noticed some
scorch marks around some of the resisters on the middle of the board.
My gut instinct is to replace the PCB again as this seems to be the
common fault with these boilers. It seems like the control is not
getting a boiler has lit signal and so switches off the gas valve. Any
suggestions gratefully received.


Amongst other possible causes - Check for a break in the ignition/flame
sense lead. A gap will permit sparks to pass but block the sensing current.

John wrote:

"Jim Thorogood" wrote in message
[snip]
At the moment the boiler
ignites and burns for a few seconds but the the green light continues
to flash at high frequency instead of going on continuously as it
should , the burner then extinguishes.



Amongst other possible causes - Check for a break in the ignition/flame
sense lead. A gap will permit sparks to pass but block the sensing current.



Yes this is the most likely cause. I had exactly the same problem with
mine a while ago and replacing the ignition/flame sense lead fixed it.

On Sat, 18 Dec 2004 11:01:45 +0000, Jeff Allen
wrote:

John wrote:

"Jim Thorogood" wrote in message
[snip]
At the moment the boiler
ignites and burns for a few seconds but the the green light continues
to flash at high frequency instead of going on continuously as it
should , the burner then extinguishes.



Amongst other possible causes - Check for a break in the ignition/flame
sense lead. A gap will permit sparks to pass but block the sensing current.



Yes this is the most likely cause. I had exactly the same problem with
mine a while ago and replacing the ignition/flame sense lead fixed it.

Thanks, I'll get a replacement lead and try it, maybe a break in the
sense lead would explain why it works for a day or so after I've had
the cover off and checked al the connections.

In message , Jim Thorogood
writes
I have a potterton suprima 60 boiler which over the last 2 weeks has
gradually got worse with the locking out problem.


. According to the fault finder
flow chart the problem is either with the PCB or the gas valve,
depending on whether there is 300vDC between red and black wires to
the gas valve. I need to get a volt meter to check this. The PCB is a
reconditioned unit from CETltd which I purchased last Winter after
similar lock out problems although last years problems were sorted out
with a new air pressure switch. When I took the PCB out I noticed some
scorch marks around some of the resisters on the middle of the board.

They're diodes and they do get hot and scorch the pcb a bit, it's normal

My gut instinct is to replace the PCB again as this seems to be the
common fault with these boilers. It seems like the control is not
getting a boiler has lit signal and so switches off the gas valve. Any
suggestions gratefully received.

Check the resistance of the gas valve solenoid (should be several kohms
IIRC, at least not open or short circuit)

Check the voltage to the solenoid - it's normally about 260 volts

Are you getting sparks from the ignition circuit ?

There are several other possibilities, so ring me and I'll see what we
can diagnose - 01923 229224


--
geoff