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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3567
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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Radiator is not getting hot even though the water is warm

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One of my radiators is not getting hot even though the water is warm in both the inlet and outlet pipes.

Hi ,lets see if we can get you sorted in the shortest possible time. Have you removed any air that may be in the radiator with a vent key?

Andrew Smith and other UK Plumbing Specialists are ready to help you
Customer: replied 6 years ago.

I have used a vent key and I thought this may have resolved the problem but didn't help.

Does the radiator have a thermostat fitted? IF so can you check that the pin is not seized by taking the head off and ensuring it moves. A small spray of WD40 would help.
Customer: replied 6 years ago.

yes it does have a honeywell thermostat which turns freely andI removed it as well to check it turns freely

It may turn freely, but the pin underneath may be stuck down, which means the valve is shut. A touch of WD40 and a small tap with a small hammer on the pin will free it.
Customer: replied 6 years ago.

Thank you for your reply can I ask you another question. when my father in law refitted the radiator after doing some decorating he had trouble turning on the outlet pipe. i checked this just now in case that wasn't open properly and the screw that locks the cap on just turns and when i took it off the bit you turn to lock off the outlet looked a little damaged. could this be the problem.

Do you have an adjustable spanner to make sure it is fully open too?
Customer: replied 6 years ago.

I do but I am worried I will damage it further as it looks misshapen already.

You can only damage it if you really hang on it. We just need to ensure it is fully open.
Customer: replied 6 years ago.

I have turned it anticlockwise and I think it is open but the rad still remains cold.

All the way anticlockwise is open. Did you check the TRV?
Customer: replied 6 years ago.

I assume that means thermostat room valve, if it does then we don't have one as all the rads in the house are thermostatic valve controlled. I have a horrible feeling after all this excellent help from you I may have to get out a plumber.

Did you take the head off the TRV and see if the pin moves?
Customer: replied 6 years ago.

Yes it I could press it down quite freely.

OK. Next step, it could be air. Go and make sure your heating is still on at the clock and the room thermostat. Next go round and turn off all the TRV's on the other radiators and see if we can force the water through the radiator that is not heating up.
Customer: replied 6 years ago.
ok i have turned all the trvs to 0
Make sure the boiler is on, the room thermostat is up and the pump is on. See if you can hear any gurgling and heat comes through to the radiator.
Customer: replied 6 years ago.

No gurgling or heat

Can you see if the pump has a lever on it, you may be able to turn up the pump speed.
Customer: replied 6 years ago.
we have a combi boiler and the only dial on that is the pressure which is betwenn 1 and 1.5
OK. The radiator is full of water. The valves are fully open. The pump is running normally. The heating is on. The other radiators are off. It should work! Let me have a read over the conversation and see if I can come up with anything else
Customer: replied 5 years ago.
Ok. I tried the last thing you suggested and no success the radiator stayed cold.
If that one radiator stayed cold whilst all the rest were off it suggests a blockage. Did the boiler make any strange noises when the heating was on and trying to pump through the one radiator?
Customer: replied 5 years ago.
Can you follow the hot pipework and see where the heat is going. Can I ask where the radiator is and how far away from the boiler it is - is it the furthest away?
Customer: replied 5 years ago.

I am not able to follow the pipework. the radiator is in the back bedroom with the boiler in the top bedroom in the loft and the radiator in question is not the furthest away

That rules out a pump problem then. The only other thing I can suggest is; with the other radiators still off, get a small tub and draw some water through the radiator by bleeding it into the tub. Turn off one valve at a time and try to get a good litre out from each time you turn each valve off. Keep an eye on the boiler pressure to maintain 1.5bar on the pressure gauge. Hopefully one side of the radiator will make a gurgling sound and will shift the air.

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