Unit Heater Cold

[Deleted member 18243]

I've got a (water-fed) Dunham-Bush unit heater which will not heat up. The fan runs but it will only blow cold air.

It is the last one on the circuit, i.e. furthest from the boiler, and the other unit heaters on the circuit are heating properly. The flow and return pipes connected to it are warm. There are isolating valves on both pipes and a drain cock on the return pipe. Both pipes are connected to the fixed pipework by flexible pipes, but these do not look kinked or otherwise restricted. Dunham-Bush's literature says that there is no air bleed valve in the unit and that bleeding should be done from the pipework above, but I can't see a bleed valve anywhere near.

What can I try?

 

[St0rmer66]

Flexi pipes are notorious for blocking up, even on an otherwise clean system. That would be my best guess.

 

[simond]

If you can isolate the others it might blow an airlock through the one you have problems with.

 

[Deleted member 18243]

If you can isolate the others it might blow an airlock through the one you have problems with.

I tried that and it worked thanks; the problem heater warmed up very quickly.

I left it running for an hour or so and then turned all the others back on, and the problem one still stayed hot.

It remains to be seen whether it will still work when they all start up together on the next cycle.