Ravenheat CSI wont stay lit

[mondeo828]

Just before Xmas the first signs of trouble were that the boiler wouldn't light at all: the fan came on and stayed on, the pump was running, the ignitor would click away, but the pilot light wouldn't ignite and the boiler would eventually trip on flame failure. Turn it all off and back on, try again and after a few goes like this it would start. Not good with 20 odd people due for Xmas day.

So I cleaned the pilot light electrode with a bit of fine emery, and checked the pilot jet which appeared to be OK, put it all back together and it fired up just fine. I checked the burner pressure and it was fine at 10mBar (mains pressure at 22mBar) and the ABV was set ok. It ran well all the way through Christmas and the New Year. Just after Boxing Day I changed the hall thermostat from a Daytron RTS2 to a Digistat 3; a very simple change-over and everything worked perfectly when I turned it back on. Until last night.

Now the pump is coming on, the fan is coming on, the pilot light is coming on, the main burner is coming on, but its then going off after 2-3 secs. Basically it just didn't want to start. This morning it ran OK first thing (at least the rads were nice n toasty when I got up) but by 8:30 it was cycling again without lighting fully. I've sat and watched the burner, and it appears to be coming fully on before it goes off, rather than not going to its second stage at all.

Its was installed about 18 months ago by me and its been faultless up til now.

 

[Agile]

If it goes off a few seconds after igniting then it sounds like a flame failure problem.

Could the main burner be deflecting the pilot flame?

Have you measured the gas pressure at the INLET to the gas valve during the fault condition with a water manometer?

Have you measured the resistance from the tip of the electrode to the PCB connection?

Do both connections feel secure?

Tony

 

[mondeo828]

I pulled the pilot light assemby, and one of the nozzles was blocked inside the jet. Cleared that and its working out now. Should the nozzle be black on the inside?

I did check the impedance for the electrode to the PCB, and it was 6ohms or so. I didn't check the gas pressure.

I do have a further question though - there is a deflectro over the top of the pilot flame, that is pointing down at about a 15-20 deg angle and the pilot flame appears "squashed", and flares out either side of the deflector/guard. Should this deflector/guard be more horozontal or angled upwards to give a (possibly) more robust pilot flame?

 

[Agile]

I would be investigating any resistance of more than 1 ohm in the flame detection path as it indicates an abnormality. As its a high impedance path it should not affect the operation but 6 ohms implies a problem which might get worse when hot.

Its difficult to discuss in words things like angles of deflectors. In practice I would use my experience of pilot flame ignition to consider making changes but the general official advice is to replace it or leave as it is.

I would wash a pilot injector in warm soapy water and a BG eng once advised boiling them. The official advice is just to replace them but thats not always practical if you dont have a spare with you. I only carry one for the Puma.

Tony