Please Help - boiler problem!

Old 04-06-06, 06:41 AM
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Question Please Help - boiler problem!

Hi - I have a combi boiler by Ariston. At the moment the pressure is fine but when the boiler is on (eg heating on constant) it is on for approx 30 secs until the temp gauge on the boiler reaches 90oC and then switches off until the temp is less than 40oC. It carries on like this and as you can imagine the house is not heating up like it should as the boiler is off half the time! Does anyone have any idea what the problem is?
Old 04-06-06, 04:13 PM
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If this is the right conversion...are we talkiing 104-194 degree fahrenheit? Not only quite the swing but quite the high temp?

By "heating on constant", do you mean like you turn up the thermostat upstairs to just let it run to see what it does? This is actually a good test as this will rule out short cycling of the upstairs thermostat caused by outside heat influences on the stat.

It sounds like you have a weakness in the boiler thermostat/aquastat. That could explain why it gets hotter than what it should, but also cooler than perhaps what it should drop down to. It sounds like it is over exceeding the aquastats set point and then 'high limiting' because of this, and then shuts down the boiler (no more flames) until the set call temperature of the aquastat is reached, for it to again start heating the boiler.

Besides the temperature, what does your water pressure reading say at cold boiler... then at 40c and then at 90c?

But what is most interesting to me is how it gets to 90c in 30 seconds, from a low of 40c. THAT has me puzzled. That is why I want you to check your pressure. I kind of think now that you don't have hardly any water in your boiler and this could explain the rapid heating AND the fact you have no heat upstairs even though you have 90 c in the boiler!
You say the pressure is fine. But what is that? And I think you might want to confirm it with another gauge screwed onto the boiler drain. (These only cost $5, plus fittings to adapt to male garden hose thread, at home centers.). There is no way a boiler should rise from 40 to 90 c in 30 seconds with a lot of water in the boiler. Not if I am understanding your post right.

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