Potterton Puma 80e - Ignition

[stu_p]

Can anybody please help? I simply can't get the boiler to ignite. When I demand hot water the modulation board does it's job, but as soon as the sequence board kicks in things go horribly wrong! It seems that I am getting a spark at relays RLL and RLT but a puff of smoke from the R1 resistor! I've done a little research and think that it could possibly be something to do with capacitor C1 or possibly the ignition electrode, but would this cause the resuistor to keep blowing? I tried replacing the sequence board (with a 2nd hand one I was able to pick up on the cheap), but the same thing happened. (It may have been previously damaged??)Does anyone have any ideas? Any help would be greatly appreciated.

 

[kevplumb]

 

[corgigazza]

Check aav is not leaking down its pipe stem into gas valve solenoid this shorts out the live to earth connections and blows the resistor sham potterton didn't fit fuse on second pcb, don't replace any more pcb until you have checked all components in boiler compartment for signs of short circuit

let us know if it works

 

[stu_p]

No joy I'm afraid. The stem of the pipe appears dry as do the solenoid valves. Everything seems to be pointing back to a new Sequence Board. Even the fault finding guide suggests Seq Board ("Fan starts before Relay 1"). I'm hoping the 2nd hand one that I got was dodgy?? Other than that I'm truly stumped.

 

[ChrisR]

R1 should be 100 Ohms. A faulty cap could fry it. The other components on the board could object to consequent spikes which aren't being snubbed!

If you can measure the components I can compare with new ones as I have spares of boards and GV. uF of Cap, Ohms of Res, and inductance and resistance of gas valve coils. Yes that's easy for me to say, I've got the kit to do it. Let me know if you needs bits.

 

[stu_p]

Cheers Chris. Yes, R1 is 100 ohms. The capacitor which it is snubbed with is a long orange thing (metallised polyester film capacitor I'm guessing?). The value on the top of it reads 680k 400'. I've tried getting hold of these via internet, etc.. and simply can't find them. Please let me know if you have any.

I definitely think I'm going to need some bits. I really think I need a new sequence board but am scared I'm gunna blow it up if that's not the source of the problem!

How would I know if the gas valve coils were faulty?

I've seen new sequence boards for £40 (all inc) which seems a fair price. I think I'd be suspect of gambling on another 2nd hand one. If you do have any unused, I would be intersested tho!

 

[ChrisR]

GAs valve coils - just put some in Deep Store (the lock-up) so don't have one handy, but coils usually measure something about a few k ohms, like 1400 or 2800 (for a Suprima, different make valve though).

C1 is 680n 400V. 680nF is 0.68 microfarads
Z = 1/(2.pi.f.C)
= 4681 ohms at 50Hz
i = 230v/4781 = 50 mA approx
FOr the resistor i.i.r = 1/4 watt, which shouldn't bother a resistor of that bulk.
Hoik a leg of the capacitor out to check its resistance is high.