Potterton Puma 100(E) Burning smell is back!!

Sorry I meant the external main switch.

It is situated on the wall to the lower right hand side of the boiler. The only reason i mentioned this was incase anyone new of any other part of the boiler in that region that might be casuing the problem.

The boilers pump is also located on the right hand side, inside the boiler casement. But having had a good sniff round the pump i have no reason to believe this is causing any problem.

Will check the mains switch again and make sure it has been screwed in properly. Will also check where the mains supply enters the boiler.

Thanks for all the help so far!
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Look at the connector strip...it's common for water to leak from the flowswitch above it and the strip to arc away.
Will take a look at the switch when I get home tonight.
A few other points I thought might be worth mentioning is that after removing the panel which covers the bottom of the boiler i noticed a build up of damp residue similar to mould forming at the rear of the panel.

Could this be as a result of some kind of leak? It looks like it has been forming for some time though, so i suspect it is nothing to be too concerned about

One further point is that the burning smell occurs when the timer turns the CH on. The problem is intermittent though and happens every couple of days rather than every time the CH comes on.
Hi, i had the same problem on my potterton puma, it was caused by the CH temp sensor leaking onto the pump the pump terminals tracking to earth, thus causing an over current demand on the pcb board and causing the PCB to overheat. if your up to it a quick test i did was connect the pump to an external supply (external to boiler) thus proving that it is the pump, if it is the pump is very easy to replace. PS remember to have the pump running all the time when the boiler is on and after the boiler turns its self off (to dissipate the heat in the system) hope it helps
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This smell is not going anywhere and seems to be getting worse.
I think I will replace the pump anyway and hopefully that will have some effect.

Thanks for your help!
If you have been working on the boiler yourself are you sure that the combustion chamber is screwed on and air tight, the spire clips are very prone to snapping. byruning smell could be products of combustion, the rattling can be linked to the spire clips. the main neutral connection on the pcb is a common problem. ensure that the wiring harness is ok.
The only work I have done on the boiler is to replace the PCB.
Will check the wire harness. Good shout.
Have tried to contact some gasmen but I can't get anyone to take a look this side of xmas!!
Further update:
I went to check the PCB for any lose fitting or loose connections and noticed as i removed the botton cover a small puddle. This I presume has been caused by a leak!

The puddle was on the right hand side where the CH flow, CH return and saftey valve pipes enter the boiler and below the rear of the pump?

Could this leak somehow be contributing the burning smell?

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