Radiators hot upstairs, but cold downstairs!!!

lambo28

Hi

I drain my central heating system to put in some Fernox MB-1 and it all went well. However, after switching on the system, my radiators are hot upstairs but stone cold downstairs.

What is wrong with it?

I am willing to work through this fault by a process of elimination! Please help

mountainchrisriver

Probably done this already but have you bled all the radiators?

bockster

maybe airlock?

i would try to turn off all the radiators and just open one cold one at a time, then the pump will be putting all its energy into one rad at a time.

by the way is the pump still running? if not upstairs rads may get hot just by convection in the pipework. used to happen with my old gravity hotwater system.

lambo28

Thanks all, yes i have bled all the radiators until the water is clear. I have also done what bockster said, but still no luck.

lambo28

I can hear the pump work away!

bockster

need to know if the pump is spinning, not just motor, the two may have seperated, doubt it but a possibility.
is it a sealed or vented ch system?

littleredhen

are they cold or luke warm - my radiators work upstairs when heating is on but if thermostat is turned down the radiators downstairs only get luke warm - if i turn thermo up they immediately start to get warmer - sorry if this sounds a bit obvious - its meant to be helpful

bockster

is it smallbore pipework to the downstairs rads only? wounder if muck has dislodged and blocked the smaller pipe? another long shot.
btw how old is the system?

lambo28

It's a vented system which was working fine until i drained the system, the downstairs are radiators are cold. The boiler and room thermostat is to the max level. Thanks

weekendwarrior

Have you checked the tank in the loft?

sometimes when you empty the system the ball valve in the tank does not let water into the tank to refill it and so it could be empty.

Normally hot rads upstairs and cold downstairs = failed pump

EliteHeat

Have you bled the pump - it won't work if its got air it it.