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Question DetailsAsked on 10/17/2015

Gas fired hot water boiler is acting up, more in details

The boiler sometimes comes on, but not always. I have tested thermostat and you can hear it click on but boiler won't start. The override switch is on. Breakers are good. I cleaned the sensor by the pilot, but it does look to have a little rusty at the top. Yesterday after messing around with it for a while, turning it on and off it came on and stayed on for hours, but also stated on longer than it should have since thermo was at 73 and went to 77. Now it won't come on (pilot still lit) but there is a buzzing as if it wants to start, when the thermostat is higher than room temp.

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1 Answer


Not sure what you mean by the override switch being on - that does not sound right, and certainly if an override swithc has to be on to make it run does not sound like a good thing to do nor possibly safe. Unless you mean the thermal reset button is in normal position, not "popped".

I would first check the battery in the thermostat is good - low battery can make for erratic operation.

Second check all 24V (thearmostat and zone valve) wiring connections for one making intermittent connection.

Third, because it went too hot and buzzes, you might have a zone valve power head going bad (assuming this is a zoned steam or hot water heating system).

Fourth, especially if buzzing is from the control box on the boiler, could be the power solenoid is going bad and not operating consistently.

Fifth - and a VERY common cause - is if pilot will light but not stay lit, or on some models pilot will stay lit for a bit then goes out, is the thermocouple has gone out - typically 2-5 year life but generally recommended to replace every year so you do not lose heat in middle of winter due to it going out. This may be the sensor by the pilot you are talking about, whcih should NOT be significantly rusty so that may be your problem - is a roughly 1/8" diameter probe which inserts or scxrews into a holder so its tip sticks into the pilot flame to tell the gas controller that the pilot is lit so it is safe to let the gas flow.

If you are not able to solve it with these tips, or not a DIY person for this type of thing, contact a Heating and A/C )your Search the List category) technician - probably $75-150 service call charge which should cover diagnosis and probably repair labor also, plus any parts needed - generally less than $100 parts unless the control box has fried (which is rare) or the boiler thermostat has failed and is integral to the control box, in which case more commonly in the $100-150 range for non-electronic, or several hundred if electronic.

Answered 4 years ago by LCD

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