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Central Heating

New ch valves - problems with flow?

Recently had my radiator valves all replaced (both TRVS and lockshields) with Draytons. Since then, the heating wont kick in unless I set the valve to 4 - at that point I can hear/ feel the water start to flow into the radiator

I have called the plumbers about this and he said that they have an inbuilt thermostat which is why theyre not turning on under 4

Im not convinced but cant explain myself properly as Im not very technical
Would appreciate any input on this
Thanks so much to everyone who took the time to answer/ makes a lot more sense now. I do find it odd however that I have 2 radiators a metre apart on the same wall. When both on: the one will be at double the output of its neighbour, and will get warm at low settings when the other doesnt. Both are same size..

4 Answers from MyBuilder Heating Engineers

Best Answer

The radiator thermostat senses the air temperature around itself and will only allow the water flow if the temperature is below what it’s set to. From memory “4” is about 17c, so it will need to be cooler than this to turn on. As it gets colder outside you will find it turns on at a lower number.


Answered 9th Oct 2019

Its important to remember the numbers on the radiator valve do not control the temperature of the radiator.
They are a thermostat that turns the radiator off when the room reaches a certain temperature.
On a Drayton valve the numbers represent a scale of 10 degrees to 27 degrees.

Instead of worrying if the radiator is hot, think about if the room is warm enough and if not set the radiator valve to a higher number.


Answered 11th Oct 2019

TRV opens and closes to the ambient temperature, the installer should have left the inlay card as this would of had the settings on against temperatures. If you are opening at 4 and theres flow, they are fine. As previously covered, when the temp drops significantly, they will open up lower and when freezing at the lowest. Still pretty mild at the moment so will notice them open morning or evening at the lowest temps.


Answered 13th Oct 2019

Dear Tina,

The Trv's has an inbuilt temperature sensor.

This sensor detects the actual room temperature.

Valve setting 3 = 19-20 degree C
Valve setting 4 = 21-22 degree C

Ex: If the room temperature is 22 or more and the valve setting is 4, then the valve is off.

Hope it make sense.



Dear Tina,

Thanks for the update.

One of the two valve heads you have mentioned is either faulty or not properly fitted.

You can swap the head valve from a different radiator in the house and see if it makes any difference.



Answered 27th Oct 2019

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