Reverse circulation central heating?

[Gareth]

I posted a while ago about radiators heating up when the central heating is turned off but just the hot water is turned on (conventional boiler).

I've realised that the radiators are also heating up - almost all of them - when their thermostatic valve is switched off.

It seems too much of a coincidence that every thermostatic valve - about 8 of them - could be faulty.

Does this sound like a reverse circulation problem?

If so is there a way of fixing it without causing too much disturbance to pipe work?

[Lieutenant Scott]

How can water circulate the wrong way when a valve is closed at one end of the radiator? You need two openings to allow the water to move.

[thirty-six]

Sounds like you are without a bypass loop in your heating circuit. Thermostatic radiator control valves do not necessarily have a positive shut-off positon and those will lift given sufficient pressure from the circulating pump.

Take the conrol head off the rad nearest the boiler, so it's on all the time, and control its actual output with a towel.

[Gareth]

Thanks guys for the replies - much appreciated.

This last comment about keeping the rad nearest the boiler on all the time has made me remember something I had forgot.

When we moved in the previous occupant had left an instruction sheet with the boiler saying one radiator must be left on full all the time (the one in the bathroom nearest to the boiler). Why would this be?

You've said the same thing. Does opening that radiator reduce the pressure flowing in to the other radiators?

[hugh]

AIUI it is normal to have one radiator without a TRV, the one in the room which contains the room thermostat. However the OPs problem is that radiators are still heating up even when the heating is switched off but the hot water is on. This suggests as someone has already said that a motorised valve is not switching properly.

[ARWadsworth]

That is one of the most stupid comments I have read on this newsgroup.

[dennis]

Typical bodge made by plumbers. What is needed is an auto bypass valve.

[thirty-six]

Explain your need for this ridiculous outburst. Forgot to take a pill?

[thirty-six]

Worse than worthless.

[Moonraker]

When the rad thermostats were supplied they should have had a cap. If you have these, remove one of the thermostats and place the cap on, screwing down firmly, this will completely shut off the radiator. Incidentally should you ever wish to take a radiator off without draining the system do this other, wise turning off the valve (as is the case with you) does not necessarily turn off the flow completely, even if it does it may turn itself on in the dead of the night, I got caught out this way once.

[Dave Liquorice]

Which is another bodge on the bodge that didn't fit a room stat to prevent the boiler short cycling once the house is up to temperature.

[JohnW]

I thought the auto bypass valves were more to allow a sink of heat for the boiler when the motorised valve closed, and would still be needed even if one rad had no TRV, as there would be no circulation path for the pump overrun.

John

[geoff]

Your post about how flame sensing works, for example

[ARWadsworth]

If you need me to explain it then you really should not be posting about CH:-)

[ARWadsworth]

Another one to add to the book.

hugh was correct.

[dennis]

Another typical ARW cockup! Nobody said hugh was wrong.

[thirty-six]

Only in that it makes balancing the sytem quicker.

[Dave Liquorice]

pressure.

Which, when doing the balancing it will have, as all the TRV heads will be removed otherwise you'll end up chasing your arse as they shutdown or open up.

[thirty-six]

After all radiators have been initially flow adjusted there is still a need to go back and check that they are performing according to the system design. A second adjustment is probable when an auto-bypass is not fitted. When there is only a minor adjustment to be made after a complete system check, then it may be assumed that the rest of the system will remain within tolerance. The auto-bypass, and a preset one is about 16quid, saves the need to even perform the first system check after the initial adjustment.

[ARWadsworth]

That does not surprise me as I have a working functional brain and you do not have anything to compare it with.