Ravenheat RSF84 cutting out

[stuart_adair]

Morning all,

I'm still having some boiler problems so thought I would come back for advice.

The symptoms are that I start the heating, the flow pipe gets nice and hot, radiators start to warm up and then the boiler cuts off after a short while, restarting after about 10 seconds. The cycle continues for about 1/2 hr but during that time the length of time that the boiler is running diminishes and the off time increases. After about 1/2 hr the orange flame fail light comes on and the boiler trips out. I reset it by turning it off and on.
The fan and the pump continue.

There are no issues with DHW and we can fill a bath of water.

Initially we thought it could be air in the system as I had not opened the air valve on the boiler but this proved not to be the case.

Next suggestion was a faulty thermostat which leads to my next question - Using a multi-meter how can I establish if its the stat causing the trip, what sort of voltages should I be measuring across the thermostat terminals.

My other thought was that the pump may be faulty and not pumping fast enough to keep the water flowing - Do pumps work slowly if they are faulty or do they just die.

Thanks in advance.
Stu

 

[stuart_adair]

I never thought I could pose a question to beat you lot ...

Stu

 

[gas4you]

If it was the pump I would expect you to have problems on dhw, as this is where the pump needs to circulate quickly to stop overheat. Saying that pump faults can have a multitude of different 'appearances'!

I'm not an expert on Ravenheat, especially without being in front of it, but I would assume that there is a ch thermistor somewhere. I would check this but sounds as though there could be a blockage in the rad ciruit somewhere. Are the isolating valves fully open?

Has this model a diverter valve or a seperate coil in the heat exchanger for dhw? If so could the main heat ex pipe work be partially blocked/scaled up?

 

[Agile]

Has this model a diverter valve or a seperate coil in the heat exchanger for dhw? If so could the main heat ex pipe work be partially blocked/scaled up?

Its actually got both !!!

The earlier 620 ones had two fluid type stats but they added NTCs to the 84 ones. One odd feature is that they dont seem to have a proper anticycling circuit. Very easy to work on though.

Although I am very familiar with this, not so wonderful, boiler, I did not reply because the OP seems to have his own ideas about how they work and whats wrong and I did not want to disillusion him !

Setting them up correctly also involves the min/max GV setting and I dont advise DIYers on that unless they are electronics engineers.

Tony

 

[stuart_adair]

Thank you for your replies. It sounds like its a problem with the system rather than the boiler itself if I read you right. I've used the original systems microbore manifolds and the original rads. Although I flushed out its concevable that there could be blockages as they are quite old. I'm in the process of changing the rads now so hopefully this solves the problem.

Stu

 

[Agile]

I never said that. You did not read what I said correctly.

However you now tell us that its a microbore system and its quite possible part or all of the problem is caused by your system resistance.

But it could also be caused or contributed to by the boiler.

Tony

 

[stuart_adair]

Apologies for not reading correctly. System resistance sounds a likely cause then. The system has a flow and return manifolds in microbore but its a very small pipe - I've replaced some radiators and 8mm microbore slots neatly over the original pipework so I think its something like 6mm.

I'm replacing as much of this old pipe as I can get to with larger bore microbore.

Why do you think it is that after a while the burn fail light comes on and the boiler trips out ?

Stu

 

[gas4you]

Tony, you say you know these boilers well, does the lockout light come on for any failure reason or is it one of those that only occurs if it is an ignition fault rather than overheat etc?

 

[werewolf]

Normally found c/h sensor to blame as they act as the duel purpose of c/h temp control and also act as boiler o/heat stat.If system sludged the sensor will soon fail.