PRISMA 24SE TURNING OFF ON DEMAND FOR HEAT

seegee · 27 Jun 2007

My PRISMA 24SE TYPE C Will start up ok when water is turned on ,then the heat will come through , after a few seconds say 15 , the flame goes off the heat will still rise and then drop back - the flame then relights to follow this cycle again

THE PROBLEM IS THE SHOWER RUNS COLD THEN HOT AND NOT AT AN EVEN OUTPUT.

when the central heating is put on the flame stops on till the heat switches the thermostat then it cuts in and out in the same fashion . the switch on the diverter works so does the tell tail to the switch the relay for the sink hot water comes on
but the one that controls the gas sol. switches off (I assume this is because either the water is getting too hot or something sensing the water is out of range?) there are two sensors the first is under the pump ,the other is by the diverter valve these are working. the end cap on the pump once undone shows the pump revolving and not under load . I have checked the air flow is clear of any blockage.

Rob · 27 Jun 2007

Plate HE is probably blocked. Best to replace but is possible to clean out although its much messier!

ChrisR · 27 Jun 2007

WOUldn't affect the CH though rob?

Has the sensor under the pump had water on it? That makes them do strange things.
The modulation of the gas valve needs checking (corgi job) but the sensor(s) would be supect too.
Tony G may know better.

Agile · 28 Jun 2007

It seems to me that he has described the correct CH operation and the only problem is what has already been suggested, a blocked plate HE.

Its easy to test that over the telephone, run a basin hot tap and see what temp the gauge goes up to. It should stabilise at about 55-60°C.

It it goes to about 70°C then there is some blockage in the primary side and if its much higher then it will need immediate attention.

Dr Margaret Busby OBE who was on R4 today has that problem with her boiler!

Tony

seegee · 4 Jul 2007

Agile said:
It seems to me that he has described the correct CH operation and the only problem is what has already been suggested, a blocked plate HE.

Its easy to test that over the telephone, run a basin hot tap and see what temp the gauge goes up to. It should stabilise at about 55-60°C.

It it goes to about 70°C then there is some blockage in the primary side and if its much higher then it will need immediate attention.

Dr Margaret Busby OBE who was on R4 today has that problem with her boiler!
seegee- if the heat exchanger is the problem and the plate is mucky then what is best practice for its inspection and cleaning also how does the gas flame check itself when the demand reaches desired temperature-it cannot just turn off it must modify its output - is this checkable say a voltage to the flame control.
Tony

Rob · 4 Jul 2007

seegee even at very low rate it can still cause the water to get too hot due to restriction. Just replace it. I wouldnt recommend a diyer to try and clean it.

gas4you · 4 Jul 2007

rob884 said:
seegee even at very low rate it can still cause the water to get too hot due to restriction. Just replace it. I wouldnt recommend a diyer to try and clean it.

1001 cleans a great big carpet, and all for half a crown

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PRISMA 24SE TURNING OFF ON DEMAND FOR HEAT

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