Upstairs radiators cold, expansion tank hot

[Briddy]

Our CH system is about 25 years old, and we've lived in the house 13 years. We've always had unreliable heat upstairs, but recently it has got worse, all the upstairs rads are now cold, with the exception of the one directly above where the boiler is, which is luke warm. The water in the expansion tank in the loft, meanwhile, is boiling hot, as are the downstairs radiators, and the hot water cylinder.

We had a new pump fitted a few weeks ago, and a new downstairs radiator, and it seems to be since then that the system has deteriorated.

I've called British Gas (who fitted the pump and the radiator, under their Service Plan agreement for free), and they came and had a look and said I needed a power flush at a cost of £515! If this cures the problem, then all well and good (though it sounds expensive), bit I'm not convinced it will, and don't want to fork out for nothing.

I did notice that on the radiator above the boiler, the inlet pipe was hot, but the outlet pipe was lukewarm. Thinking this implied there was a blockage in the radiator, I took it off and jetted it out. The water was black, but no heavy sludge and no blockage, and since putting it back there's no difference. The pipes on all the other radiators are cold.

All help appreciated, particularly if it saves me £515!

 

[30kw]

Your system is pumping over and drawing in air causing corrosion and sludge problems, may be due to a number of things. These include pump location, open vent and cold feed location. Ideally on a fully pump system the flow from the boiler should go to a closed couple cold feed and open vent, basically the 2 pipes are near each other. Trace the pipe route from your boiler and in the airing cupboard and back.

An air seperator can help, this requires configuration work dealing with pump relocation.

Ask British Gas to supply a quote for reconfigure pipework in airing cupboard and air sep, this should be a cheaper alternative.

However a Powerflush may still be needed to rid the entire system of corrosion/sludge, to enable continued problem free running, ie no rads pin holed.

 

[masona]

You can hire a power flushing machine approx £50 a day if you want to diy

 

[oilman]

This won't cure all your problems, but the pump probably has a 3 speed selector on it and I bet it's set at 3. Try setting it at 2 and see if things improve.

 

[30kw]

Dependant on the system, pump speed isn't a matter, i expect its a grundfoss/myson pump installed, on setting 3, putting on number 2 may stop pumping over initially but wont rid the problem, extending open vent can help too, its hard without seeing the installation really and making a valid judgement but i suspect configuration problems with it being an old system.