Upstairs fine, downstairs mainly cold

[DGClarke1]

I have a Vaillant 30Kw System Boiler. It's a fully pumped and pressurized system.

There is a hot water storage tank in an airing cupboard upstairs, with a single zone valve that allows hot water into the entire CH system, or stops it.

All the upstairs radiators get hot, but only a very few of the downstairs radiators do. The pipe on the flow side of the circuit coming down to feed the downstairs is very hot, but the return is only luke warm. ]

If you feel the valves on the radiators downstairs, they are hot on the flow side and cool on the return.

The 28mm flow and the return pipes from the boiler to the airing cupboard are both hot.

I would appreciate any thoughts anyone may have on this.

 

[SimonG]

Circulation issue. Could be a failing pump or sludge or issue with rad valves.

 

[PlumbBobBob]

Circulation issue. Could be a failing pump or sludge or issue with rad valves.

I agree

 

[joni os]

Common problem in autumn, after heating been shut down for summer. Sludge in system, sticking TRVs and motorized valves not fully opening. A rebalance of rads may be necessary, but 1st get circulation going by manually opening motorized valves, removing heads of trvs on cold rads to ensure pins move freely and close down hot rads to force circulation through the remainder, even if it means having only one rad open at a time. Very often once circulation is restored, nothing else is necessary, apart from making a mental note to chemically clean and flush system at a time convenient to the household and whilst heating is still in use.

 

[JCplumb]

In my experience, cold down and hot up almost always means the pump's gone.