Potterton Puma 80e - problems igniting

[GeeTee]

My Potterton Puma 80e keeps going to lockout when trying to ignite. However, if I keep pressing the reset button it will eventually light - sometimes takes 10 minutes or more of resetting for it to fire.

This is worse in the morning when the system hasn't been used for several hours. If it's only been a short time since it was last used the boiler ignites straight off.


As per the Fault Finding in the manual.....

Yes the red light comes on the modulator board
Yes the fan comes on
Yes there is a good clean spark
Yes the overheat stat is closed (put a multimeter across it to check)
Yes there is continuity across GV1 and GV2 solenoid valves

That's where the troubleshooting ends...


Another odd thing is the DHW flow at the tap. Before the boiler fires the flow rate is quite poor. When eventually it does fire there's a sound from the boiler like something filling up and the flow rate at the tap increases significantly.

Once fired up and hot the DHW flows about 9.5 l/min which is about right for this boiler.

I'm at a bit of a loss here. As it is sparking I suspect it is something to do with the Gas Valve. But why would it eventually light and be fine if that were the case?

I notice the GV3 solenoid has a circuit to the overheat stat, is it possible that although the stat is showing continuity that the resistance through it is too high? Anyone know what it should be?


I have no intention of messing with the GV and it's an expensive part to replace! So any ideas would be great...

Cheers
Graham

 

[ChrisR]

Another odd thing is the DHW flow at the tap. Before the boiler fires the flow rate is quite poor.

That's the easy bit, it's meant to do that - water saving until it's hot.

Non ignition is to do with a few things like dirt, intermittent gas valve operation, maybe HT short, but all are Corgi territory. A normal service should sort it.

 

[GeeTee]

I just thought as it seems fine once it's been used for the first time in the day it's most likely temp related. Hence the question about the overheat stat.

Straightforward enough to get at and relpace - just thought it might be worth doing before shelling out.

Cheers
Graham

 

[ChrisR]

The problem may well be temp related, but a OHstat is just a switch, which should be nearly zero ohms when shut. Haven't seen one go high resistance so far.

 

[GeeTee]

OK, thanks.

I measured across both the OH stats and yep 0 Ohms.

I guess I'll be getting Mr Corgi out

Cheers
GeeTee

 

[GeeTee]

Further update on this....

I replaced the ignition electrode and HT lead (as they only cost small change) - it didn't make any difference but I did notice something else whilst doing it.

When the sparks are on I noticed a clicking noise from the Full Sequence Control Board - on closer inspection it sounds like there is a spark discharging inside the what I presume to be the ignition coil (black box marked T1 on the board that connects to the HT connector).

Is it normal for this to click whilst sparks are being generated?

I'm applying car logic here, but surely the only discharge should be at the ignition electrode not in the coil?

If not can this part be obtained individually and soldered in place or will it require a whole new board?

Thanks again

Graham

 

[ChrisR]

The coil could be making a click without a spark. There's some phrase like magnetic relaxation - the plates/wires of the core physically move a bit.
Officially you can only change the whole pcb - sorry I mean a corgi reg...
The boards are around pretty cheap though.
If you've got a fat spark I wouldn't worry.

 

[GeeTee]

Is it only a corgi eng who is 'allowed' to change a PCB? I thought the restriction was only on gas carrying parts

I better not have taken it out to check the solder joints then had I

I think I'm going to have to admit defeat (and stop being a skinflint) and get an engineer out.

I can get the board for about £60 (inc VAT), but it's a bit pointless at this point I think. As you say it is sparking - but then applying my car logic I've seen plenty of misfires and poor running caused by dodgy coils / HT leads whilst they appear to have a 'fat' spark at the plug.

Anyways, thanks for your help.

Cheers
Graham