One upstairs and one downstairs radiator cold

[redwhite]

I have two cold radiators. 1 is upstairs and the other is downstairs. It is a fairly new house (three years old) although I only moved in a few months ago.

I have bled all the radiators.

I have shut off all warm radiators and opened all cold radiators but they still do not warm up.

The outlet valve does not seem to be stuck.

Any suggestions would be welcomed, thanks.

 

[MANDATE]

Do you have a by pass valve? If you do and it is not closed sufficiently water will take the easiest route and avoid going through radiators, leaving those furthest away from the pump cold or just warm.
Do you have TRVs on the radiators that have been closed for a while, they can become stuck in the closed position?
Are the feed pipes at the base of the radiator hot.
Don't forget each radiator has two valves, the inlet may be fully open but what about the lockshield valve, that may be restricting flow

 

[redwhite]

I'm not sure whether or not there is a by pass valve, where would it be? The other radiators in the house are ok.

There are TRVs on all the radiators and I have taken the plastic knob off to check if they are stuck - they seem to be ok as i can press them down and they pop back up again.

The feed pipes at the bottom are cold.

The inlet is fully open, the TRV valve on the outlet is also open as far as i can see.

 

[Softus]

Shut one valve and open the other.

Open the vent into a bucket or tray - does the pipe to the open valve get warm?

Repeat the test using the other valve - does the other pipe get warm?

 

[redwhite]

shut one valve then opened the other. bled through vent, water came out. no heating of pipes observed.

shut open and opened other valve. repeated above. still no heating of pipes observed.

 

[Softus]

How much water did you let out of the vent?

 

[redwhite]

about a mug full

 

[Softus]

You need to collect the same amount of water as the amount of cold water in the pipework between the distribution circuit (usually in 22mm) and the branch to the radiator tail (usually in 15mm).

For every metre of pipe, you need to draw off about 0.15 litres of water, so one mug full might be a bit borderline.

 

[MANDATE]

by pass valve does not have specific location, but would be in a branch off pipe after the pump. Have you any gate valves that you don't know what they are for.

 

[Softus]

Also, when you did the closing-off-all-rads-except-for-the-cold-one test, did you put the pump on maximum speed?

 

[redwhite]

i dont know how to alter the pump speed, but i put the thermostat right up.

i've just drained about 1 litre of water from the radiator, still no heating at all.

 

[MANDATE]

Pump should have lever on the underside (with markings 1, 2 and 3). Turn lever to select speed.
Apart from by pass valve being open too much, are the two cold radiators linked. If the upstairs one is directly over the downstairs one and both fed from a branch pipe off the main flow and return pipes. It could be an air lock in one of the branch pipes.
Does the upstairs radiator have a drain cock at one end. If so drain off from that with one valve closed, then repeat with other valve closed as suggested. This should release any air locked in the flow and/or return pipe.
As far as I can see if it's not closed valves, I can't see it being a sediment blockage and a open by pass or air lock seems to be the only other explanation.
You could remove the upstairs radiator and then run off a bucketful of water from each side in turn. I did this only last week, only to find there was no air lock or blockage and the same problem as yours was caused by a open by pass vavle. If only I'd investigated that first!