Gravity hot water heats upstairs rads when on.

[pieceofmind]

This seems to be a design feature (our next door neighbour's identical setup does the same thing) but can it be designed out? It's really irritating to have to go around all the upstairs rads and lock them off at the start of summer, then open them all up again at the start of winter.

The boiler is an oil-fired Potterton Statesman Utility. CH is pumped but HW is gravity. It's all drained down at the moment whilst I attend to another issue, so it might be a good time to attack this problem if it's possible to do so.

Cheers!

 

[stem]

You probably don't have a motorised valve to shut off the pipework feeding the radiators. Although the pump won't be running some natural circulation is probably still occurring, so with heat rising the upstairs radiators get warm when the boiler is 'on' & heating the hot water.

I had a similar problem in a house I bought 22 years ago. There was more pressing work needed at the time of moving in, so to start with as a quick fix, I just fitted a two port motorised valve just after the pump to stop gravity circulation around the radiators. Only a minor wiring modification was required.

A few years later once the more pressing repairs were completed, I converted it to a fully pumped S-Plan system with two motorised valves, a cylinder thermostat, plus a new room thermostat and programmer, to give totally independent control of the heating and hot water. The whole system had to be rewired at this point.

 

[ianmcd]

sounds like the return from the Gravity HW is connected in the wrong place

 

[pieceofmind]

You probably don't have a motorised valve to shut off the pipework feeding the radiators. Although the pump won't be running some natural circulation is probably still occurring, so with heat rising the upstairs radiators get warm when the boiler is 'on' & heating the hot water.

I had a similar problem in a house I bought 22 years ago. There was more pressing work needed at the time of moving in, so to start with as a quick fix, I just fitted a two port motorised valve just after the pump to stop gravity circulation around the radiators. Only a minor wiring modification was required.

Does the pipework 'split' into separate HW and CH somewhere after leaving the pump? If so where might I find that split? I can't see anything like it, but then my pipe disappears into a wall within a couple of feet of the boiler

 

[stem]

Mine was something like this, with the hot water one side of the boiler with 28mm pipe and the heating on the other with 22mm pipe. However, yours could well be different, you may even have a one pipe system if it's very old.

My pump was on the return so the motorised valve was added just after it. If your pump is in the flow, then you need to make sure that whatever you do leaves the vent pipe unobstructed.

 

[pieceofmind]

Mine was something like this, with the hot water one side of the boiler with 28mm pipe and the heating on the other with 22mm pipe. However, yours could well be different, you may even have a one pipe system if it's very old.

View attachment 167687

My pump was on the return so the motorised valve was added just after it. If your pump is in the flow, then you need to make sure that whatever you do leaves the vent pipe unobstructed.

As you've probably worked out I'm no plumber, but that diagram seems to show the HW and CH as totally separate circuits (unless they mix inside the boiler)? If that's the case what does the valve do?

 

[ianmcd]

yes they should be separate systems, can you post a pic of the pipes leaving your boiler please, not convinced you actually have a Gravity HW system

 

[pieceofmind]

There are 3 pipes leaving the boiler. 1 bottom left, 1 bottom right, 1 upper right.

 

[ianmcd]

that is not a gravity HW system, it may be a F&E tank fed system which some confuse with a gravity DHW system, but that is a fully pumped system,wouldnt be surprised if it is a total bodge up, but definately not gravity HW

 

[stem]

In that case, if it's fully pumped, I wonder why only the upstairs radiators get hot, and not the downstairs?....unless the downstairs radiators have TRV's and the upstairs don't.

Edit:
pieceofmind, I've just seen your photos in another thread. On this thread you say that

There are 3 pipes leaving the boiler. 1 bottom left, 1 bottom right, 1 upper right

So what about the 4th pipe from the top on the left hand side?

From the photos I would expect your system to be something like below, in which case, that looks pretty much the same as my original sketch to me. [except the hot water is on the left and the heating on the right] and if it is, then you can add a motorised valve, with some minor pipe modification.

 

[pieceofmind]

My god I'm blind as a bat. So sorry. How does putting a valve in there stop the upstairs rads heating up when the HW is on? To clarify there are no TRVs on ANY of the rads! Or are only the upstairs rads heating up because some sort of thermosiphon effect?

 

[stem]

Based on the original description you gave of three pipes, it would appear that the system could be fully pumped, and I suspect that's why @ianmcd said that. But if that was the case, that means that the pump would run when heating the hot water cylinder, in which case all of the radiators would get hot, not just the upstairs, so that is why I questioned it.

If it was fully pumped it may have been possible for the downstairs radiators not to warm up if they were fitted with TRV's which had closed because their set temperature had been reached. But as there aren't any TRV's you can ignore that theory.

So, I now believe that you do have a gravity hot water piped to the left hand side of the boiler, and pumped central heating connected to the right hand side. [you should confirm this is the case] in which case often only the upstairs radiators warm up under gravity circulation. Fitting a motorised valve will close the heating circuit when the heating isn't on so no water will circulate through the radiators.

 

[pieceofmind]

OK thank you for clearing that up. Is there any reason not to fit a valve BETWEEN the boiler outlet and the pump, as that's the only bit of pipework I can access (see pic). From the pump outlet the pipe runs behind the boiler and into the wall and there's no room to even get a cutter or soldering torch to the pipe, let alone fit a valve.

 

[stem]

Normally, the motorised valve is located after the pump. Probably because there are usually two, one for the heating and one for the hot water, both of which have to have their own independent feed from the pump. Although I don't believe there would be a problem with fitting it before the pump in your case, as there is just the one motorised valve. I've no doubt that someone will say otherwise if not. [I'm an electrical engineer not a heating engineer, and my knowledge of heating systems comes from working with my father who was a plumber many years ago, and knowledge picked up from wiring up heating systems]

Personally, I would do it by moving the pump further away from the boiler to make enough room below for the valve, something like this:

The motorised valve contains an integral switch (connected to the grey and orange wires) so that the pump only operates when the valve has physically opened, so the wiring would be:

Whilst this modification stop the radiators heating up by gravity circulation, you could consider having it converted to a fully pumped system, to provide independent time and temperature control of the heating and hot water. The building regulations require this to be done when a new boiler is installed, so assuming you plan to keep the hot water cylinder, it will have to be done at some point in the future anyway. However this is not usually a DIY job unless you are very competent and fully understand the plumbing and wiring systems involved.

 

[pieceofmind]

Thank you very, very much for taking the time to help me with this. Whilst I have your attention do you have any thoughts on a good location for a magnaclean, given the space constraints around the boiler? Does it have to be located right near the boiler?