I have a 2 storey 3 bed house with 4 radiators upstairs and 4 downstairs. The system is about 15 years old and is a standard boiler downstairs with a hot water cylinder upstairs.
The upstairs rads all heat up as normal but the downstairs ones remain stone cold. We have attempted to balance the system which has had no real effect to the downstairs. The pipes going into the rads downstairs are hot but there appears to be no flow into the rads as they are still cold. I've removed 3 of the rads d'stairs and the water coming out has only a small amount of suspended black debris coming out. An inhibitor has been added which i picked up in B and Q which stopped the rads being stone cold but they are still not heating up - as if there is still no flow through them.
When i took the rads off i turned the TRVs on and there appears to be good flow coming from them which suggests to me that the pump is functioning and there is nothing wrong with the supply flow.
When i then put the rads back on and bled them to fill them up they got hot as they filled but cooled down soon after as if the water wasn't flowing out of the rads.
The only thing i can think is that there is a block somewhere in the return pipes.
Can anybody shed some light as the 3Kw heaters are getting expensive!!!