Central heating problem - flow hot, return cold?

[gdickin2]

Hi, having problems with the central heating - all the rads in the house are lukewarm (nearest bolier) to cold (farthest from boiler).
I have got a Vaillant ecotec 937 combi. The thermostat is demanding heating and the boiler fires up and heats up to the temp set on the heating dial on the boiler. After a while the burner lock out time kicks in. There are no errors on the boiler and the pump active indicator is on.
The CH flow pipe from the boiler is hot to the touch but the return is nearly cold.
I have a Magnaclean on the return which I have stripped down and there was hardly any build up on it so doesn't seem to be blocked in there.

The symptoms are indicating that the pump isn't working but as I said above, there are no errors and the pump active indicator is on.
Could I have a blockage somewhere in the rad pipe network?
Would a full drain down be worthwhile?
Any other suggestions of things to try?

Many thanks for any tips.

 

[Agile]

It certainly sounds like a blockage!

The only problem is knowing where!

I suppose you could add X800 and run the heating for four hours before draining.

But you may well need to call an engineer as it might be a blockage inside the boiler.

Tony

 

[gdickin2]

Thanks Tony, resigned myself to having to call the engineer out. Just have to be cold for a few more days.

 

[Agile]

Why do you need to be cold for a few days?

If someone called me out then I would expect to come and fix it the same day!

Tony