I have just moved house and have problem with gas fired central heating. Radiators are getting hot when 'Hot Water Only' is selected on programmer.
I thought this may be due to pumped water leaking past one of the motorised valves when it should be closed (a problem I have had before) but the pipe coming from the valve is cold on the outlet side but the radiators are still getting hot! Is it possible for the pump pressure to cause the water to reverse flow or something?
Otherwise, anyone any ideas what might be going on here? All help gratefully received and thanks in anticipation :(
Thanks for your response. Sorry, for lack of info but I'm no expert here! Don't know if it will help but I can try and describe the system to you. Firstly, its in a house and boiler is downstairs, wall mounted. It's not a combi boiler (tank in airing cupboard). There is a header tank in the loft (I think this means that it is not a sealed system?).There is a pump in the airing cupboard feeding from the boiler. This then branches two ways to 2 x 2 port valves. When 'Hot Water' is selected on time switch one of the valves opens and feeds to the hot water tank. When 'Central Heating' is selected the other valve opens and feeds to the radiators.
As I said in my earlier post, I assumed that the problem must be a faulty valve allowing water past when it shouldn't. However, the outlet side of the valve feeding the radiators remains cool when 'Hot Water' only is selected, yet the radiators continue to get hot. I hope this helps and I would appreciate any advice. Thanks.
Your description seems as if the system is a standard "S" plan with the two valves, one as you say to control the hot water, and the other for the heating.
Also, your presumption that the most likely culprit for the problem is as you say, the valve. If the valve is fitted in the return pipe, the water may feel cold because of the flow from the radiators. In that case the valve may still be leaking.
If we discount the valve, the fault is far more obscure, and will be difficult to identify at a distance. First to consider is some of the rads may have been deliberately plumbed in before the valve or in the hot water circuit to provide heat when only the HW is on. Maybe some rads have been accidentally plumbed into the system before the valve.
Probably the most likely culprit is the bypass. To operate safely, a way of ensuring some circulation of water is still possible in the event of the boiler and pump are operating but both the motorised valves are shut.
The bypass normally is a short length of pipe linking the flow and return pipes and has a gate valve fitted to regulate flow. This gate valve should only be open by one full turn (approx). You may find this valve low down near the cylinder and quite separate from the normal isolator valves from the header tanks. Do not confuse the valve with the restrictor valve fitted in the primary hot water circuit where it connects to the cylinder coil.
I can't check out the things you suggest until next weekend as we haven't properly moved in yet. However, whatever happens I will post a message either to let you know I have sorted it, or requesting more of your kind help (I suspect the latter being more likely). If I have to engage a professional to sort it, then so be it. I will however let you know. Thanks again.
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