Hi my ravenheat 85 a works fine when asking for hw however when the ch is demanded sometimes the burner will ignite, burn for 20 seconds or so, then extinguish.
After 2 or 3 seconds.It will reignite and cycle like this maybe 8 times, then it settles down and works normally until the room stat shuts it down.
Any ideas out there what may be the problem ?
Cheers
billthespark

billthespark, November 2008

Thanks Josh,I have measured the HW thermistor, i'm getting 9.4 k/ohms when the system is cold,so I tried a 9k/ohm resistor across the ch terminals,to prove it.The system still cycles even with the fixed resistance in place.and the therm' drops down to approx 4.5 k/ohms
One other thing is if I run a hot water tap for a few seconds the burner stays lit and the CH works until the room stat shuts it down!!!!
Any ideas are welcome its doing my head in.

billthespark, November 2008

Thermistor//

Joshmcfee, November 2008