Downstairs Radiators Cold

10 Oct 2005
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United Kingdom
This is a simailr problem to others already posted so my apologies in advance for any duplication.

I seem to have two problems:
1. Downstairs Radiators not getting hot
2. Central Heating switching off when Hot Water turns off

I am trying to understand how the system is supposed to work and then hopefully work out what is wrong to fix it.

The equipment is as follows:
Barlo Blenheim Boiler
UP1L Programmer (British Gas)
ACL Lifestyle mid postion valve
Grundfus pump UPS 15-60
Room Thermostat
Frost Thermostat
Tank Thermostat
4 x radiators downstairs (2x small, 1 x large, 1x large double)
6 x radiators upstairs (3x small, 2 x large,1 x towel)

Things tried so far:
All radiators bled - little to no air came out
Pump removed and checked for blockages/operation - appears ok
Pump bled - ok
Pipework adjacent to pump bled - little to no air
All radiators shut in and then downstairs radiators brought on one at a time at approx 15 min intervals - each radiator initially got hot as they were brought on, however the larger radiators began to cool slightly as each of extra radiators came on. It was possible to have all of the downstairs radiators on when the upstairs were blocked in, though the large ones were not as hot as normal.
When the upstairs radiators were opened up the downstairs radiators immediately began to cool off until eventually they got cold.

I have been trying to draw out the control circuit for the system but whilst I have been able to bell out all of the cables so know where they come from and go to, I have been unable to find any wiring diagrams for my boiler, the mid position valve or my controller and can therefore only guess how it is all supposed to work.

Any help or advice would be much appreciated


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Thanks for the advice....

I have tried the pump on all of the different speeds and it doesn't seem to make any difference.

I have also tried to balance the system (without thermometers, so it was a bit of a guess) but as I started at the radiators nearest the pump i.e. the upstairs ones it meant that I had no heat in the ones no this the right way to do it?

Thanks again

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Your second problem 'central heating switching off when hot water turns off'
Although I'm not too sure of what you mean in detail, it does sound like it could be the usual mid position valve problem.
When the demand is for both HW and CH the valve takes up the mid position. When one of the requirements is satisfied the valve moves either to HW only or CH only. Moving to HW only rarely is a problem but moving to the CH only positon does have it's problems and you may not realize what's happening. One minute you have CH and then you don't, It works ok so long as you are demanding HW but not on CH only.
The problem can be related to the valve not moving or not moving far enough. Or if it does move to the CH only position it may not provide the power needed for the boiler/pump.
A stiffish spindle offers resistance so you need to ensure it is free, also if you can verify the valve has not moved the full amount then a replacment motor may be the answer.
If the valve does move the full amount and the boiler does not function it is probablely a faulty microswitch.(check voltage on orange wire)
The basic wiring for a mid position valve.
Wire from cylr. stat. T1 (calling for heat)goes to orange wire on valve then on to boiler/pump
Wire from cylr. stat. T2 (no call for heat)goes to grey wire on valve
Wire from HW OFF also goes to grey wire on valve
Wire from room stat. goes to white wire on valve.
Does that help.
:rolleyes: :rolleyes: :rolleyes:
Thanks for the advice...........I will give it a try tomorrow and see if I can discover anything


Once you've fixed the 3-port valve problem you may find the rad balancing becomes much easier, so fix this first.
Do you have a 22mm gate valve on the hot water cylinder return so this can be balanced also? If not you'll get low flow to the rads at mid position, OK when water is hot.
Unless you have microbore pipework the Grundfos 15/60 pump will easily handle the loading of your rads, probably at speed 2.

Nice initial post, lots of good background info without the waffle. :D
Thanks to everyone for your advice.

The problem was the valve sticking and only partially opening up to the central heating circuit. I removed the motor and exercised the stem a few times and it loosened up nicely, this gave me almost instant hot radiators throughout the house. I have tried to balance the system now and seem to have all radiators working ok.......have switched it all off for the moment to allow it all to cool down, then I will fire up the central heating again to see if there are any problems.

Thanks again


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