Combi boiler switching itself off


Postby maxdecatt » Fri Dec 17, 2010 4:29 pm

I have a Grandee wall mounted combi boiler, not more than 5 years old.
It works well but sometimes seems to have a mind of its own.
After weeks of trouble free operation it will just switch off.
Then once I have restarted, it will opeate without a problem.
It is in my garage and the temperature in there seldom drops below 8C.
Recently the boiler has sometimes switched off when domestic hot water is called for. At other times it switches off when the radiators call for heat, depending on the time settings for the radiator heating to come on.
I have adjusted the thermostat in the garage to 9C and more often than not that works perfectly....but it is erratic and I have come home sometimes (after the pre-set radiator switch-on time) to find the system has shut down. I start it again and can then go a week or longer before the boiler plays up again. Last night everything was fine until I tried to have a shower....the hot water was excellent for a couple of minutes.....then went cold and I found the boiler had shut down. I turned it on again and it has operated perfectly for the last 24 hours.
Is the problem connected with either of the following??
Can demand for domestic hot water trigger a shutdown?
Can, as apparently sometimes happens, a shutdown be caused by the heating programme asking for radiator heat?
The thermostat in the garage is a Drayton RTS3. It clicks when I turn it and I understand that is an indication it is working???
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Postby stoneyboy » Sun Dec 19, 2010 6:48 pm

maxdecatt,
Intermittent faults are an absolute nightmare, you can call in a gas-safe techy but if there is no fault any repair will be pure guess-work.
end
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Postby maxdecatt » Mon Dec 20, 2010 12:29 am

stoneyboy wrote:maxdecatt,
Intermittent faults are an absolute nightmare, you can call in a gas-safe techy but if there is no fault any repair will be pure guess-work.
end


Yes, I know! I have had the original installer out to look at it a few times and everytime he 'finds' the fault and swears it is fixed. Parts are replaced and hiss bills are presented and paid....useless.
I suspect it is something to do with the temperature sensors....either in the boiler or with the room thermostat. Is it possible to wire the room stat incorrectly so you get odd on and off behaviour?
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Postby stoneyboy » Tue Dec 21, 2010 2:42 pm

maxdecatt,
You haven't said but I assume the boiler is oil fired.
The thermostat in your garage is a frost stat and this should be set at about 5 deg C.
The intermittent fault could be from a number of causes. Is there water in the oil line? Could be the geometry of the burner head is incorrect........
What has been replaced to date?
end
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Postby maxdecatt » Wed Dec 22, 2010 1:07 am

stoneyboy wrote:maxdecatt,
You haven't said but I assume the boiler is oil fired.
The thermostat in your garage is a frost stat and this should be set at about 5 deg C.
The intermittent fault could be from a number of causes. Is there water in the oil line? Could be the geometry of the burner head is incorrect........
What has been replaced to date?
end


The boiler is oil fired.
It was installed on8 August 2006.
So far the following parts have been replaced by the installer as he has tried to sort out the shutdown problems:
* RF thermosate and control unit in the house.
* Auto Air Vent on boiler.
* Oil filter on supply line.
* 10 litre expansion vessel.

As previously said, the shut-downs are erratic, the last one was 4 days ago. At other times they can happen 4 or 5 times a day for 3 or more days in a row.
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Postby stoneyboy » Wed Dec 22, 2010 1:04 pm

maxdecatt,
Please explain what you are doing when you have to restart the boiler.
Do you depress the button on the control box or do you do something else?
end
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Postby maxdecatt » Wed Dec 22, 2010 8:09 pm

stoneyboy wrote:maxdecatt,
Please explain what you are doing when you have to restart the boiler.
Do you depress the button on the control box or do you do something else?
end


All I do is press the re-set button on the cabinet. It is situated below and between the two indicator lights. (When operating only the left hand button glows. If the boiler has switched off both lights are glowing.)
On pressing the button ONCE the boiler immediately starts.
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Postby maxdecatt » Wed Dec 22, 2010 8:14 pm

stoneyboy wrote:maxdecatt,
Please explain what you are doing when you have to restart the boiler.
Do you depress the button on the control box or do you do something else?
end


I can add that the last sh-down (after a few days of many such events....4 or 5 per day) the boiler has operated faultlessly for the last 5 days!
It is this erratic behaviour that causes concern...I feel I cannot go away overnight without worrying about possible freezing if the thing stops operating.
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Postby stoneyboy » Thu Dec 23, 2010 2:13 pm

maxdecatt,
From your description you are resetting the high limit lock-out switch as opposed to the burner lock-out switch. If this is correct I suggest you get the high limit stat replaced.
end
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Postby maxdecatt » Thu Dec 23, 2010 7:48 pm

stoneyboy wrote:maxdecatt,
From your description you are resetting the high limit lock-out switch as opposed to the burner lock-out switch. If this is correct I suggest you get the high limit stat replaced.
end


Thank you. Looking at the manual I note that the High Limit Thermosat is on the front of the cabinet (this is what I have been using to re-start).
I did not know about the Lock Out button (and the engineer has never mentioned it) which I see from the manual is located under the unit (the unit is the wall mounted type).

When next the unit fails I will try the newly discovered Lock Out Button.
Thank you for your help. I will let you know what happens.
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Postby stoneyboy » Mon Dec 27, 2010 11:03 am

maxdecatt,
The two reset buttons are independent of each other. The high limit reset button is tripped by over-temperature in the boiler, the burner reset button is tripped by a fault in the burner control system.
end
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Postby maxdecatt » Mon Dec 27, 2010 5:02 pm

stoneyboy wrote:maxdecatt,
The two reset buttons are independent of each other. The high limit reset button is tripped by over-temperature in the boiler, the burner reset button is tripped by a fault in the burner control system.
end


Thank you.
Why my installer has never mentioned this ...or even alluded to it....is a mystery to me. Probably because he is keen to have as many call outs as possible!
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Postby stoneyboy » Tue Dec 28, 2010 12:29 pm

maxdecatt,
Before you get the high limit stat replaced try turning the boiler to a lower temperature on the control stat - it could be this is faulty and allowing the boiler to get too hot.
I don't think any of the replacements you have had in the past would correct the boiler going to high temperature lock out. Did you show the installer which button you have been using to resart the boiler?
end
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Postby maxdecatt » Wed Dec 29, 2010 1:09 pm

stoneyboy wrote:maxdecatt,
Before you get the high limit stat replaced try turning the boiler to a lower temperature on the control stat - it could be this is faulty and allowing the boiler to get too hot.
I don't think any of the replacements you have had in the past would correct the boiler going to high temperature lock out. Did you show the installer which button you have been using to resart the boiler?
end


I will try reducing the temperature.
He has never even mentioned that there was a reset button on the underside of the boiler! Just told me to push the one on the front.

I was wondering, when a trip-out occurs (there has now not been one for 10 days!!) and the 2nd light illuminates on the boiler.....would it illuminate irrespective of it being the high limit reset.... or the burner reset.... that is the problem?
What I mean is, does the light indicate a particular area fault or just that the boiler has switched off?
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Postby stoneyboy » Sun Jan 02, 2011 9:32 pm

maxdecatt,
The second light on the front of the boiler shows that it has turned off due to the boiler reaching a temperature above the setting of the high limit stat. There is no link to the boiler control button ie you cannot reset the boiler control by pushing the button on the front of the boiler.
end
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