Why do Radiators warm up when the hot water is on?

OK I'm no expert but I will try to describe this problem as best I can:

The central heating system in our house is a fully-pumped, open-vented Y-plan system. Now it should be possible to have either the central heating or the hot water on separately, shouldn't it? The problem we are experiencing is that the radiators start to warm up when only the hot water is on.

I should point out that we only moved in a few weeks ago, and that the previous owner of the house when contacted said it had always been like that.

After reading around, it seemed to me that it was obviously the three- port valve that was faulty. Even though I'm a novice, I thought that to change the valve was a pretty easy job, so I had a go myself. So I drained the system (I now know that was a bad idea) and successfully put a replacement valve in. However, when I went back into the loft to turn the cold water feed to the header tank back on, it turned out that the tank was already full.

At that point I was stumped, so called out a professional; at first he thought it was simply an air lock but later found that one of the pipes to the air separator had become blocked with sludge. He cut out and replaced that bit of pipework, which allowed the system to be filled back up again. (He also advised me that I shouldn't have drained the system - the three port valve can be changed just by inserting a couple of rubber bungs into the pipes to and from the header tank).

However, when the system was tested out the radiators were still warming up with the hot water. The heating engineer could not work out why, at first he said I'd put the new 3-port on backwards, but after checking, it was correct. The wiring also seems to be correct, and the valve seems to be switching over correctly.

So he finally concluded that something was causing the heat to flow from the boiler return backwards to the radiators, and that I needed a one- way valve putting in somewhere. He left me with instructions to pull up the floorboards and investigate where the central heating pipes run.

Before I start pulling up floorboards, are there any clever people here who might be able to help explain what's going on? Could it be that the system just needs re-balancing? I notice that at some time someone's added thermostatic radiator valves to the bedroom radiators, could this have anything to do with it?

Reply to
Miles
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pluber brother in law : "there's a lot of heat to dissipate, it's got to go somewhere"

hth

RT

Reply to
R Taylor

From your original post, it appears that you've got a Y-plan system, and that you've already replaced the 3-port valve - so we have to assume that that isn't faulty.

I suppose that it *could* be wired wrongly - so that the valve always thinks there is a CH demand even when there isn't.

It seems more likely to me that the whole system is *piped* wrongly. Hot water should come from the boiler outlet, through the pump to the inlet of the 3-port valve. One outlet from the 3-port valve should go to the inlet of the coil in the HW cylinder. The other outlet should go to the inlet (flow) side of all the radiators. The outlets from all the radiators should be connected together, and taken back to the boiler inlet. The outlet from the HW coil should also be taken back to the boiler inlet. If the HW and CH returns are connected together, this must *only* be done after the point where the *last* radiator return connects in. If there are radiator returns

*either side* of the HW return, you have a possible return path that goes through some of the radiators - even with the CH port on the 3-port valve closed. I suspect that this is what is happening.

Under these circumstances, the radiators won't get as hot as they would be with the CH on, but they will get distinctly *warm*. Does this fit the facts?

If this *is* the problem, you need to correct the pipework rather than faffing about with additioanl valves.

Reply to
Set Square

"Set Square" wrote in news: snipped-for-privacy@uni-berlin.de:

I'd think the wiring has a good chance - if Miles copied the wiring, and did a good job, he would have transferred the fault that pre-existed, and it's a lot easier for an earlier DIYer to mess up the wiring than the pipes.

mike

Reply to
mike ring

Reeminds me of a bloke who asked me to look at his car - battery was going flat.

I discovered some current drain with ignition off.

Fuse pulling seemed to indicate the circuit with the horn and a few other bits in.

Then I noted his tootle trumpets, and a relay 'Oh, I fitted that - it was a kit, you connect it to the horn push, the horn wire and the horn - works fine' (deafening me with demonstration)

Of course the horn push conbncted to a relay contact, not the coil, and the other side of the relay NO contact went to the horn and the relay coil was wired across to earth, so the relay was permanetly on drawing current, and the horn push operated the horn through the now permanently closed contacts.

'oh, is that all it was' he said as he steadfastly refused to pay me for my time and expertise.

Wanker.

Reply to
The Natural Philosopher

The Natural Philosopher wrote in news:ckpmsu$n96$1$ snipped-for-privacy@news.demon.co.uk:

t

Gives you the right hump, doesn't it? I expect it happens to all of us who know a bit about something or other.

And somehow the b***s make it seem that it's *you* who's the know-nothing twit, or is it that we're just the oily rags (bitter memories of broadcastin days.

(love your new handle)

mike

Reply to
mike ring

Thanks, that's very helpful, and yes, the radiators do not get as hot as when the CH is on. Also, it is only mostly the upstairs radiators that are getting warm, some of the downstairs ones remain cold.

So it sounds like I do need to investigate where the pipes are running to confirm this problem. I think I will check the wiring first, as the other poster said, just in case, because it's a lot easier than pulling up floorboards.

I don't know if this is a bodged former DIY job or a design fault when the house was first built ~10 years ago, because like I said, the previous owners (who were in 7 years I think) said it has always been like this.

Reply to
Miles

By all means check the wiring first - that should be quick to do. However, my hunch is that it *isn't* the wiring. If it were - such that the valve was being driven to the mid position when it should be in the HW-only position - I would expect *all* the rads to get hot, and to get fully hot - not just warm.

It could be an original design fault or a DIY bodge. It probably only needs the return from one radiator to be connected *after* the HW return. If someone has added a radiator . . .

Reply to
Set Square

Sounds like the zone valve may be in the return, rather than forward path of the pump, or it may not be fully closing.

Or there is a bypass or some such, and the rads are getting a slow gravity feed.

My old house was a bit like that - one rad near the boiler used to warm up regardless of anything. It was the bathroom rad, so I left it that way.

It may be no more complex than the CH primary pipes running alongside and heating up the CH pipes, and gravity flow does the rest.

Reply to
The Natural Philosopher

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