If I want to force pump to direct all its attention to radiator in loft to see if I can get them hot. Will simply turning down the thermostatic valves for all the other radiators have that affect or do I also need to close the lockshield valves as well

Edit, update explanation of my system

I am based in Uk with three storey house. I have a 2 year old Worcester Bosch 24R Boiler, There is a 22mm supply and 22m return copper pipe round along the first floor floor joists from left to right through the house, with a pump on the supply pipe near the boiler. The supply pipe serves both the Central Heating and Heating a regular Hot Water Cylinder, I can control whether to use CH, Hot Water or both, there is a T-valve near the the hot water cylinder that controls this.

On the first floor there are 15mm copper pipes that come off the 22m supply and back onto the return, the same downstairs. Evey radiator has its own loop.

The only slight problem with this arrangement is that the T-Valve is positioned after two downstairs radiators have been supplied, so unless I turn them off they are always heated even if only specify Hot water.

In contrast there are two radiators on the 3rd floor (but still top of radiator is 1.5m below feed/expansion tank in loft) supplied by plastic pipe, although it doe seem to also be 15mm. What I can see is there is one set of pipes shared between the two radiators so I guess this halves the flow immediately ?

What I cannot readily see because I would have to remove bathroom laminate flooring is where they join the 22mm pipe, there is a possibility that they are sharing a loop with bathroom radiator.

The radiator that I described as further away, and you say nearer is physically quite far from the boiler (i.e start of 22mm supply pipe), but is probably nearest to somewhere along the 22mm supply pipe. So what is (most)important , distance to start of supply pipe or distance to supply pipe ?

I did consider whether to replace the plastic pipes with two set of pipes and that would be quite easy, however there would still be a short run under the bathroom floor of one 15mm pipe to the 22mm pipe, so if any of the pipe run is shared would that mean having two sets of pipes further up would have no effect.

All of the radiators and valves have recently been replaced ( 2 weeks ago) so there is no issue with sludge in bottom of radiator and unlikely to be problem with valves. Actually last night one of the radiators did get warm (but no hot) throughout, but the other failed for warm at all. I bled them again and there was no air, there was water.

  • You should be able to get away with turning down the thermostatic valves as that will reduce flow rate through the radiator. No Flow , No Heat,.
    – Ken
    Dec 4, 2017 at 9:05
  • I think I get it now, so the whole central heating circuit is full of water. When you turn it on then boiler will start heating and pumping it along supply pipe. If a thermostatic valve is closed then the route from the supply pipe to that radiator is closed so then the water cannot flow along that spur pipe and finds another pipe of less resistance and so on Dec 4, 2017 at 9:42
  • yes - the valve controls the flow .. temp reached no reason to allow the heat to be exchanged in the radiator to the air - (NO FLOW).
    – Ken
    Dec 4, 2017 at 9:45
  • Slightly confusingly the radiator that seems to heat up the quickest seems to be furthest away from boiler but I wonder if that is because we have a 22mm supply (and return) pipe, which goes down to 15mm for the loops that attach to the radiators. The radiator furthest away form the boiler is very close to supply and return pipe so the length of 15mm pipe used in his loop is smaller, does that mean that therefore its resistance is the lowest and that is why it heats up quickest ? Dec 4, 2017 at 10:04
  • The one furthest away is not furthest away from the boiler connection wise, it is first according your comment. The water in the system here will be hotter and will cool as it travels down the line. Think about turning on your hot water faucet furthest from the Water Heater. The pipes closest the heater will get hotter sooner. d.george has relevant information, depending on what exactly you really are trying to do, why.. Is the problem No Heat in Loft, no flow to loft radiators and therefore you want to force.. the question is important to determine - Therm valve issue or No/Low flow issue.
    – Ken
    Dec 5, 2017 at 1:27

1 Answer 1


If you are not getting heat to the radiators in your loft area, the problem is probably not enough system pressure. GO to the loft radiator and open the vent. you should get water out of that vent or air first then water. If you do not get water out of that vent, you do not have enough system pressure. Go to the boiler and check the system pressure. If the system pressure is 10 psi then the water in the system will be 23.1 feet high. (1 psi = 2.31 feet high). You could measure from the top of the highest radiator to the pressure gauge and divide the distance in feet by 2.31 and get the required system pressure, and add 2-3 psig for safety. From your writing, I will guess that you have what is called a monoflo heating system. If that is the case then poor installation practices may cause one radiator to heat quicker than the others. By the way, where are you located since you are using mm instead of inches as we use in the USA. (0.0999Kg/CM2 = 1 meter) You should not have to close off 1 radiator to get heat somewhere else. All radiators should heat at about the same time.

  • To add to my post, depending on the actual piping arrangement, you could also have a direct return or a reverse return system. The reverse return would be the best for overall operation , but is rarely used in a home due to increased cost of installation. None of us are there so telling you exactly how your system does or does not operate is a little difficult. We can only guess based on what you tell us.
    – d.george
    Dec 5, 2017 at 11:53
  • Ive updated my question, if monoflow is what is referred to in UK as one pipe system then no I have two pipe system. I cannot see pressure gauge on boiler so I'll wait to see for you to digest my updated question before doing anything. Dec 5, 2017 at 12:55
  • So flow to radiator is affected by its positioning, and pump doesnt solve this ? Dec 5, 2017 at 13:02
  • Follow the supply and return pipes to the end of the run. Are they 22mm to the end of each run or do they reduce to a smaller size somewhere along the horizontal run? Does each supply just stop at the end furthest from the boiler or are they connected together at the end of the run. Were the 2 loft radiators recently installed and do you know if they ever heated. Do you get enough domestic hot water? Your last statement about positioning--the radiators position in the system (how far it is from the boiler) matters. You may need a pump with a higher head if the 15mm pipes are too long.
    – d.george
    Dec 5, 2017 at 17:16
  • 1
    The loft radaitors were not added recently, but since they are the only part of the system to use plastic pipes I suspect they were added to the system later than the rest. They have never worked much, but then many of the radiators have not worked well until I replaced them. I tried basic radiator balancing because i noticed that the return of some radiators was nearly as hot as the supply indicating to much of the suply routed through these ones. That has balanced the other raidators out a bit, bit not made much difference to the loft ones. Dec 5, 2017 at 17:38

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