Two rads not working, one up one down

[prydien]

I think this is a simple problem to solve. I have one rad upstairs and one downstairs that are stone cold - not even warm at the valves. They used to work when I moved in but have not worked since I drained the system to fix a leaky rad valve. I have drained the system dosed with sludge remover refilled bled rads and drained and refilled and bled rads again but still no joy. I have balanced all the other rads to allow more flow for the faulty ones - no joy. After it refills the faulty rads get a little warm in one corner but soon get cold again. I start bleeding rads from upstairs first this is right isn't it? I have even fitted a new pump. The only thing I have not done is remove the rad valves and check for blockage. If they were blocked would the pipe work before the valve be hot? Another problem which I am sure is related, is the header tank is filling with hot water from the expansion pipe. This gets worse if I turn the pump on full. The boiler stat is turned down low and works fine. From what I have learned it looks like the pump may be in the wrong place. It looks as if it is fitted in the pipe that comes down from the header tank (top up pipe? not the mains feed) and its under the cross over pipe (between the expansion pipe and the top up pipe). Of course I may be wrong. Not a plumber as you can tell. The system was fitten in early 80's.
Hope you can help. These two rads are driving me up the wall.
Regards Peter.

 

[corgiman]

do you have a thermostatic rafd valve if so it could be stuck off, or alternatively one off the rad valves might not be working (ie shut off) which would explain why its bleeding ok but not circulating

drain it down again and have a look

 

[prydien]

Hi thanks for the reply.
There are no TRV's. If a rad valve is blocked or shut then would the pipe be cold before the valve? Would this be the cause of the header tank filling with hot water? When I get time I'll drain down and check the valves.
Regards Peter

 

[oilman]

As you can tell, it's "pumping over" turn the pump down to start with. It seems suspiciously like an air lock. It's unlikely to be the valves. Have a search on the net for central heating circuits, the pump could be in a poor place. Are you bleeding the system with the pump off?

 

[prydien]

Are you bleeding the system with the pump off?

When I refill the system I have been waiting for the header tank to fill then bleeding the first floor rads then the ground floor. Then running the pump and bleeding the rads again in the same order. The pump is on the lowest setting. It is positioned between the motorised valve and the crossover pipe. (by this I mean a short 4" section between the top up pipe and the expansion pipe) I expect I`m using the wrong terms here.[/url]

 

[masona]

Agreed with the above,sounds like you have a air-lock as it was okay before you repairs the leaking radiator.I think you got to start again,turn off the main feed supply to the expansion tank,open up motorized valve to manual,drain down system again,when finish draining the water,shutdown your drain point then open the radiator bleed valve nearest to the drain point, then open up the water supply to expansion tank,but don't wait until the expansion water filling up,go down to the lowest radiator & bleed,hoping it will push the air out both way then bleed each radiator backward from the drain point,when finish put the motorized valve back to auto position.