Removing an overtemperature thermostat.

My oil fired boiler has an over temperature thermostat (copper capillary with bulb) which is stuck fast in a steel pocket. It is now tripping regularly. I have found this occurs after the bulb (complete with a coil of copper tube) becomes rusted into the pocket.

My query is how do I free things up and return the operation to normal, or indeed get the damn thing out to replace it! Apart from a pistol drill with attendant risk of damaging the pocket, is there any magic releasing agent that will eat the rust and leave the copper bulb free?

Andrew.

Try one of the rust remover/nut unlocker sprays, perhaps allowed to work for a few hours then followed by a freezer spray which will loosen the copper in the steel.

Neil

(I'd like to apologise to the ozone layer for the above...)

If there is enough of the copper jacket left to grip, I suggest getting hold of it with long nose vise grip / mole wrench pliers, then tap backwards on the locked pliers with a small hammer or tap on a screwdriver held across the jaw opening. Lots of small taps on the pliers, and wiggling of the jacket, will likely get it out.

When you replace it, use some good quality anti-sieze compound or PTFE thermal transfer grease down the hole and on the jacket and bulb before fitting the new one.

If you don't mind draining the boiler then get a new thermostat pocket as well as the thermostat.

Unscrew the pocket, throw it away and fit the new one.

When you install the new copper bulb, may i suggest coating it liberally with Vaseline/grease/

1) This will give good thermal contact

2) The grease, should greatly reduce the risk of rusting. (Probably caused by atmospheric moisture, when the boiler is cold leading to electroytic corrosion. Don't know what bthe voltage of a Cu Fe cell is!)

Howard

Thank gentlemen,

I don't think the pocket is replaceable, so I shall try all the suggestions!

Many thanks,

Andrew.

Andrew,

Just abandon the present thermostat and fit an external type that straps to the outside ion the tank.

Look at "Drayton HTS3 Cylinder Thermostat" only £15.99 from Screwfix.

Eric

Thanks Eric,

I have one of those on my copper hot water tank. I didn't realise that it was capable of 95 degrees centigrade. Must check it out.

I might have difficulty in getting the spring around the boiler, but worth a try.

Thanks,

Andrew.

Thanks Eric,

I have one of those on my copper hot water tank. I didn't realise that it was capable of 95 degrees centigrade. Must check it out.

I might have difficulty in getting the spring around the boiler, but worth a try.

Thanks,

Andrew.

Andrew,

Why on earth would you want your boiler heating water to anywhere near 95 C under any circumstances.?

The normal water temperature produced should be 65C max. so an over temperature thermostat should be set at say 70C perhaps 75C absolute maximum. Human contact with water or radiator surfaces greater than 65C will cause scalding and is therefore dangerous.

I strongly advise you to seek the advice of a competent heating engineer who has experience of your particular type of heating system.