CH Problem - 2 radiators hot, rest competely cold

[markelane]

Hi,

I've been reading the advice issued on this forum avidly and have tried all suggestions concerning (the many) similar problems and plenty more besides. As a last resort I am posting in the hope that someone can shed light on the problem.


Firstly the layout

- 2 bed semi, 2 up 2 down with single storey extension at rear housing kitchen and bathroom

- Gas CH via back boiler (Gloworm) in living room. (Hot water completely separate water heater in kitchen)

- 2 rads upstairs, 3 downstairs (1 in bathroom)

- All rads have thermo valves apart from bathroom

- Cistern in loft with cold water riser and tap

- Pump under floor boards in living room about 2 feet from boiler


The problem

- 1 downstairs rad (in the same room as boiler) gets hot properly, bathroom does too

- All other 3 rads (2 upstairs and 1 downstairs in dining room) do not get hot. And I mean not hot at all. Completely at ambient temp, flow or return pipes not hot at all

- Last year both upstairs rads worked perfectly. However the downstairs dining room rad has never got hot since I moved in (it did used to get a tiny bit warm originally though)

- I think the rad in the lounge is the first off the circuit

- The bathroom rad is off a drop from upstairs and therefore has it's own drain cock

- I believe the boiler is working correctly (that is, stat calls for heat, boiler runs until return water is hot enough then stops. As water cools, boiler comes back on)


What I have tried already

- Bled all rads several times

- Drained whole system down twice

- Had all rads off wall and flushed through (suspecting blockage in rads). Water a little black but no sludge

- Have had lockshields and thermo valves off and blown air through return and feed pipes with a little bit of hosepipe. This blows out the drain cock after a little residual water

- Have run water (from garden) hose through return and feed pipes. This drains out of the drain cock clean water, and smooth flowing after a short gurgle

- Turned off all rads except one of the problem ones and ran system for a few hours with stat on max


All of these things have been done over a few weeks and without exception the result is identical. The living room and bathroom rad are hot (very) the others completely cold. Not even any convection heat on either of the pipes.

I am now completely out of ideas for what to try next. I first suspected air in rads, then sludge, then an air lock but feel I have investigated these and need to go to the next stage.

Any suggestions and ideas from people in the know would be very very welcome!

Cheers
Mark

 

[ChrisR]

There's a house for sale in my road. (Just though you might try moving?)


That was a joke. Is this a new /sudden problem? ie did it just get worse this year?
Try pump on full if you haven't, and just ONE rad upstairs, open. What then?
You migt have an anti-gravitycirculation one-way valve in the pipe somewhere. Blobby brass thing. Could be stuck.

Pump has to be suspect, sometimes they have od things happen like the rotor comes unglued, or they go at half speed.

Could still be sludge - old flakes. Suggest you remove pump and look for correct operation, and sludge in there. You could take the head off the pump (2 or 4 allen screws) - assumin gthe valves work. If they're slotted 1/4 turn types they will leak and need replacing.

 

[breezer]

what about bleeding the pump?

 

[ChrisR]

Yep, worth a try. Not usually a prob when they're at the bottom of the house though.

Make sure the pumps the right way round, too.

 

[markelane]

Hi guys,

Thanks for the response so far.

Re: the question about being a new problem; the downstairs dining room rad has never got hot since I've been here (just over a year). Last winter all other rads worked really well including the 2 upstairs. So yes and no - yes the upstairs rads are a new problem, no the downstairs one is not.

Re: the pump; yes I think that will be the next step at the weekend (floor has to come up ). Will inspect as per the suggestions

Re: anti-grav valve - where would this most likely be? Ground or first floor? Near the pump/boiler?

Re: pump right way round - which way should it push the water? i.e. should it push hot water round, or pull it?

Really appreciate the input so far. Could a failed/partially failed pump produce these symptoms? I thought that mostly failed pumps mean that rads upstairs get hot via convection but not downstairs.

Cheers
Mark