Potterton Prima F 40 boiler with a 407677 PCB, the resistor R15 between the relay and the pressure switch connector block, is seriously looking overheated, can anyone tell what the value of this resister is and maybe a code for it when buying in Maplins, so I can replace please

Nigel, March 2010

I can't say if it's a lasting "fix" - the 407677 along with most other boiler PCBs I assume, uses Electrolytic Capacitors. These things tend to fail especially in warm environments - and it gets warm inside a boiler case.

The capacitors cost just a couple of £ from Maplins etc and only take a little while to replace - for the sake of saving the cost of a new PCB it's a worthwhile thing to do if you're confident with a soldering iron and understand which way round to fit the capacitors.

If the fault is down to the caps then new ones will last as long as the old ones did - more or less.

The burnt resistor may not actually need replacing - a nice thing to do rather than an essential thing - the designer just got the wattage a bit wrong - a burnt resistor may still be good - just blackened.

I am not a heating engineer - I used to be a computer engineer long, long ago.

A "savvy" boiler engineer might save up several of these defective PCBs and replace the caps and R15 himself -

An "ethical" boiler engineer would sell them on at a generous 50% discount if they worked.

Peccavi, March 2010

does changing resistors and board components work well or for long? ive allways replaced the whole 607477 and havent gone back to any yet but they cost 120 pounds plus vat each

john, March 2010

100K I believe - you are not the first - search on here for R15 or for 407677

I think your boiler will work without this resistor - I have a strong feeling it's just a bleed resistor across the main gas valve to make it close quickly - permanently taking current as long as the boiler is on it gets too hot and burns a bit - if you do replace it use a higher wattage.

Reference to it in this thread...

http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler

Good luck...

Peccavi, March 2010