Radiator thermostat query

[galaxi]

A couple of the radiators in my house have a Danfoss Thermostat on them (not sure exactly which model of the thermostat but by the looks of them both I'd say *at least* 10 to 15 years old). Both are turned up to maximum.

It looks similar to this:

mine is of a slightly older design. The principle is the same though.

Anyhow, the one in the hall works fine - the radiator stays on all the time and it gets nice and hot and stays that way until the heating goes off. The one in the lounge comes on okay when the heating fires up (twice a day) but then goes off when the room reaches what it thinks is the 'correct' temperature - the thing is I'd like it to stay on all the time that the heating is on. (Note: there is another radiator in the lounge that does NOT have a thermostat attached and that stays on all the time of course).

Is the thermostat likely to have developed a fault? Short of replacing it, is there anything I can check? I've tried twiddling the setting up and down, etc but no luck. Don't they have some kind of pin inside that governs whether the water flows or not based on the temperature? Perhaps this is sticking at a certain point so causing it to switch off the water flow incorrectly?

Thanks.

[galaxi]

BTW, on the Danfoss website, the type that I linked to the picture of is listed as being for the 'commercial market'. The current sensors they list are the RA2000 range.

[Harry Bloomfield]

galaxi was thinking very hard :

The one which shuts the flow off when the room achieves the set temperature is working exactly the way it is designed to work. If the room is still cold, the head might be faulty.

If the head is removable, then it should be possible to remove it leaving the radiator with full permanent flow, as you say you would like it to be.

[john]

"Thermostat" - a device to control heat by turning a device on or off in response to the needs of the environment.

Why would you want it on all the time if the room has reached the desired temperature? Try using a thermometer in the room - perhaps you have bcome accustomed to liking the room to be getting constantly warmer (like my wife). Bear in mind that there will be a bit of a lag before it opens the flow again. eg - if set to 21 degrees - that is where it will close - but the room may have to cool by just over a degree to open it again (Hysterisis I believe this is called)

John

[galaxi]

The room isn't cold, but it's certainly not as warm as we'd like it to be.

I see, thanks. I'm not sure how to remove it though. Any ideas please?

I notice that at the rear of the sensor there is a small (about 3mm) allan key head and near that a number moulded into the black metal that says: 88P (the one in the hall has 82P on it). Obviously not the price ( ;-)) but a model number perhaps?

I've looked and looked but can't yet see any instructions for this on the 'net.

[galaxi]

That's just the thing though - the room, in our opinion, has reached the desired temperature *but* then it seems to drop a bit yet the radiator in question stubbornly stays off.

Possible I guess, I'll have to hunt down a thermometer to check that.

I see. Okay, thanks - will check the temperature.

[Harry Bloomfield]

galaxi formulated the question :

If you unscrew the allan screw, the head should then slide off. Under the head there will be a small peg. The peg operates the valve and should be free to move about 1/8 inch. If not free it off. If you pull it all the way out water will leak out, so be carefull.

[Harry Bloomfield]

galaxi presented the following explanation :

There is bound to be some temperature overshoot, until it settles down.

That would be the best way, rather than guessing.

[galaxi]

Sorry for the late reply - I'll try your suggestion, thanks.