Towel rail not getting hot at top.

[triphazard]

I have a heated towel rail in upstairs bathroom. (Gravity fed system) the top of the rail does not get hot when the heating is on. This can be temporarily remedied by bleeding the air out of it however the next time the heating comes on the same thing will happen. When the heating and pump is off, if I bleed the rail there will be little or no air in it. I can't understand why air appears in this rail (which is the highest point in the circuit) but only when the heating is switched on. Any one in the know?

 

[lightning]

You could fit an auto air vent on rad, your need to check why system is drawing in air.

What pump is set at, is vent pipe correct height , where is the pump on the system

Paul

 

[triphazard]

Thanks Paul

I have an auto vent fitted but it only seems to work if I close the return valve on the rail. When I do air will come out and the rail gradually gets warm at the top. Pump is set at 2 (used to be 1 before I changed all the rafiators and changed all the pipe work from microbore to 15mm. All the rads are piped to a manifold in the floor void. The pump is on the return adjacent to the boiler. Not sure about if the vent pipe is at the correct height though.

 

[Madrab]

If you don't have an obvious leak then it may not be air, hold a flame at the outlet when you have to bleed and see if it light/burns, if so it's hydrogen and an indication of corrosion within your system. Note that it may burn with a blue, hard to see flame, so the darker the better.

 

[triphazard]

Thanks rob I tried that and no reaction to the flame. Will try again in a darker room though to make sure.

 

[dominoman]

It does sound like air is getting in somewhere. Double check that the F&E tank has water in it - especially when cold.

If not that then check the cold feed from the F&E to the system isn't blocked.