Ravenheat HE85T (CSI85T) Not Firing

[andrew_c]

Please, I know these boilers get a load of stick but I'm stuck with one and could really do with some help!

I woke this morning to find my boiler ignition failure light blinking. Turning the power off and on didn't fix it and the pressure in the system is fine at 1 bar.

The boiler currently does the following:
- DHW is called for.
- Water pump runs.
- Main PCB fan relay clicks on and off about 10 times (one every 2 seconds or so).
- Water pump stops 20s later.

Now this would immediately make me think that the fan relay was broken but... when I remove a wire from either the overheat stat, low water pressure switch or flow switch, this happens:
- DHW is called for.
- Water pump runs.
- Fan runs.
- Fan and water pump stop 20s later.
- Red ignition failure light blinking.

The process of operation on this boiler is meant to be Pump, Sensors, then fan. So I'm not sure how removing one of three random sensor wires allows it to continue.

This has been exhausting checking that every sensor I can get my multi meter into. I'm only a little unsure about the pot values. I got about 17Kohm on both the CH and DHW pots. The overheat stat was shorted (not sure if this is right?).

I've also replaced the fan control board with a spare I repaired a while back (I tested it after repair and it worked back then).

Please, if there is anything I've missed, lemme know!! It horrible sat here in the cold

Thanks guys,
Andy

 

[picasso]

Check the condensate trap and sensor.

 

[andrew_c]

Hey there,

The condensate trap looks half full but doesn't have any sensor plugged into it?

 

[picasso]

Sorry thinking of wrong boiler.

 

[andrew_c]

Actually, I've rechecked what sensors cause the fan to spin up constantly. It's actually just the overtemp stat. Unplugging the others just stop the fan relay trying to click in.

I'm wondering if it's actually the stat that's got a weird intermittent fault where by, at rest it's got continuity and passed the multimeter test, but... when power is through it, the stat is faulty and sets and resets itself over and over tripping the fan process on and off?!

 

[andrew_c]

IT WAS THE OVERHEAT STAT! A paperclip has saved the day. I'll replace it ASAP Thanks guys.

 

[lightning]

So you have bypassed a safety device ????

 

[andrew_c]

So you have bypassed a safety device ????

Yessum a faulty safety device. The boiler has been left switched off after testing. I've just nipped out and paid £20 for a new sensor (grr wish Amazon had it on Prime).. fitting will commence imminently.

Cheers!