Can't drain down under gravity

[alban]

Hi
Have tried to just drain down open system after putting in Superfloc. I get good flow from drain with pump on but it diminishes and stops long before even F&E tank empty (ball valve restrained) when pump off. I drained from lowest point on system (a drain point on a cul-de-sac to the cloakroom rad) and opened upstairs rad bleed valves. Boiler drain cock doesn't want to budge despite some real effort and I'm a litttle chary of forcing it and having to replace it suddenly! I think that's the only other drain point. Er...am I missing something simple?
Cheers
Grahame

 

[croydoncorgi]

Er- did you open the bleed valves on the rads, starting upstairs?

 

[brumylad]

is there a motorised zone valve in the system

has the feed pipe from the expansion cistern become blocked with sludge so it now appears it is not draining ? check for iron sludge were the feed pipe meets the system with a magnet (it should NOT stick).

opening any manual air vents may help.

If your desperate, try back filling the system by conecting one end of a hose to the drain valve and the other end to a mains tap (double check valve protected of course), this might shift any blockage. This will fill the header tank of course, so careful you don't bring the ceiling down by over doing it. Check the system has a vent pipe before you do this, if that blockage won't shift, you don't want to subject the boiler heat exchanger to mains pressure.

 

[alban]

Thanks
Yes opened upstairs bleed valves on rads
There are 2 mot zone valves.
F&E empties when pump running so exit prob not blocked?
Re using mains pressure do you mean doublecheck there's a valve protecting the mains water supply? Is a vent pipe the one that hangs over the F&E tank? If there's a vent pipe is it difficult to damage the heat exchanger?

 

[brumylad]

There are 2 mot zone valves.

flick the lever over to manual and hook it over the stop on both valves

doublecheck there's a valve protecting the mains water supply

close......protect the cold water supply from the central heating water using a doublcheck valve.........if u want to be ultra PC

Is a vent pipe the one that hangs over the F&E tank? If there's a vent pipe is it difficult to damage the heat exchanger?

yes and yes