Powermax 140 CH Pump Running but Heating Not Circulating

Hi,
I have a Powermax 140 installed in a flat. I removed a radiator whilst decorating and drained the system down at the same time, via the removed radiator. I refitted the radiator and filled the header tank. When bleeding the radiators I The noticed they seemed to fill very slowly (very liitle noise of air venting). The header tank is normal and all radiators trickle (not spurt) water at the vent screw.

I turned the heating on, selecting HW+CH. The boiler fired up and heated the HW. Thermostat was turned up and the CH pump runs.

The radiators however do not get warm. I removed the CH pump screw and a small amount of water trickled out. The pump spindle was confirmed to be rotating and both pump valves open.

The CH flow and return connections and immediate pipework at the boiler are hot. Pipework downstream of the CH pump is cold.

Any ideas on why there seems to be no flow and the rads are cold?
Cheers

this is typical of a blocked feed pipe. There is enough water in the system for it to work, until you take off a radiator and lose a bucketful of water. Then the blocked feed does not fill the system again. It is frequently noticed after taking a radiator off for decorating or repair.

The blockage is most often black iron oxide in the Tee where the Feed pipe from the feed and expansion tank in the loft joins the larger circulation pipe, most often close to the pump and/or cylinder and/or boiler. If you hold a strong magnet to this joint, you will find it is attracted to the copper pipe due to the black iron oxide deposits inside. The iron oxide comes from the steel radiators corroding due to lack of inhibitor in the water.

When you looked in the F&E tank, was there mud at the bottom? When you took the rad off, did black sludge run out?

Hi, Thanks for the reply.

The F&E tank is not very accesible as its positioned at the top of the boiler cupboard, so I could not check for slug.

When I removed the radiator I flushed it out, the water was black but not sludgy.

I recently bought the flat, which is about 9 years old and I doubt it had much TLC in those eight years.
I will try the magnet test you mentioned tomorrow and report back.]

cheers