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?

Miles wrote:
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.


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

hth

RT

In an earlier contribution to this discussion,
R Taylor wrote:

Miles wrote:
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.


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

hth

RT

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.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"Set Square" wrote in
:


RT

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.
this fit the facts?

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

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

mike ring wrote:

"Set Square" wrote in
:


RT

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.
this fit the facts?

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


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.


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.

******.



mike

In article , says...
In an earlier contribution to this discussion,
R Taylor wrote:

Miles wrote:
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.


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

hth

RT

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?

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.

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

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.

In an earlier contribution to this discussion,
Miles wrote:


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.

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 . . .
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Miles wrote:

In article , says...

In an earlier contribution to this discussion,
R Taylor wrote:


Miles wrote:

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.


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

hth

RT

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?


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.


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


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.


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.