Ravenheat CSI 85 boiler shuts down

[frendzarin]

My 7 year old boiler has started to shut off before the rads have got to the required heat,i.e. the room thermostat is (at 18C) still asking for heat from the boiler I have replaced both DHW &CH thermistors,and for good measure also replaced the reset cut out situated far left on the front panel,still the same thing occurrs boiler kicks off for about 10 or 15 minutes then shuts down as though it is overheating,seems like the upstairs rads are hot & down stairs only warm ,has been like this now for a while nowhere near as efficient as it once was, a pal of mine suggested it could be a pocket of trapped air ,the thing is where?, I have bled the rads a thousand times,has anybody had any similar promlems like this ,any help on the matter would be very much appreciated,thanks.

 

[gas4you]

Whats it like on DHW?

 

[Agile]

I would first be checking the pump as in the finger test in the FAQ.

Although first I would have measured the flow and return temperatures just before it shut down!

Tony

 

[frendzarin]

After loads of head scratching ,eventually found out that this boiler has a system called auto venting at the top inside the boiler itself,I was told this could be blocked with limescale and not allowing air out from the highest point ,lo & behold when I removed the small brass float chamber,it was well blocked with a reddish hard scale ,soaked the thing in limescale remover overnight ,its now working as back to nomal thank god ,its been bloody cold of late round here,goes to show that the smallest thing can create the biggest problems .

 

[Agile]

I think the auto air vent is INSIDE the combustion chamber on your boiler.

Only gas registered people should be opening the combustion chamber!

I am surprised that the blocked AAV was having such a significant effect although if it had allowed air to get into the pump then there would be little pumping action.

That amount of air would never normally accumulate unless you had been draining the system or individual rads.

Tony