Getting HW when only CH is on and it's not the valve???

[ragj195]

Hi

I've got a vented system. It's a very only setup and up until 2 weeks ago i only had one two port valve. Because the rads were heating up when only HW on the timer was on I assumed the valve had gone. Rather than replace the valve I went for a 2 x 2 port salus valve kit and paid for it to be fitted. The CH engineer noticed a 15mm pipe coming from the HW circuit going up to the ground floor ceiling. He said that must be for a bathroom rad so that it's hot in the summer when just HW is on.

After a few days I've noticed that the rads are heating up when just HW is on and CH is off. CH valve is not hot and is closed. So it seems this 15mm pipe for the bathroom rad is actually heating other rads.

I then turned HW off and CH on. CH valve opens, HW valve shuts. After a while that dam 15mm pipe starts to get hot!!! There must be some sort of link. All I want is for the rads not to heat up when just HW is on so that I don't have to close them all in the summer. Could I just cut the 15mm pipe and cap each end so there is not way HW on the outside of the HW valve can get into the CH circuit?

Thx

 

[Armo74]

Could be a by-pass, if not you need one on an s plan anyway.

 

[D_Hailsham]

Was the original valve in the CH or HW circuit?

Was it in the flow or return?

Does the bathroom rad heat up when only HW is on?

Turn CH only on and check which valve gets hot first on each rad.

Turn HW only on and repeat the check.

 

[ragj195]

Was the original valve in the CH or HW circuit?

Was it in the flow or return?

Does the bathroom rad heat up when only HW is on?

Turn CH only on and check which valve gets hot first on each rad.

Turn HW only on and repeat the check.

The flow came out of the original boiler then split, with one 22mm going to the cyclinder and the other to the 2 port valve which went on to the CH circuit.

Everything heats up when HW only is on even the the CH valve is definitely close. Although some rads don't get very hot.

I'll do the check and post back. Thx

 

[oilhead]

Back feed from return?
Ask your installer to check.

 

[D_Hailsham]

Back feed from return?
Ask your installer to check.

That's why I asked the OP to check which pipes heat up first.

 

[ragj195]

I haven't managed to turn the heating off and do the tests yet. What I did do was make sure HW was off. Empty the HW cylinder until it runs cold then wait with only CH on. After 60 mins the HW tap was warm. I knew something was up before because I never had a cyclinder stat until one was fitted last week. It was set to 70C so for the first time the water wasn't going to be steaming hot. However because of this issue it still is.

It's a 1930s house and the boiler is an old Potterton (late 70s). I paid the heating engineer to fit the 2 x two port valves and a cylinder stat. What he's done is working fine. As this is more about the pipework it doesn't really relate to his work but he said he'll take a look next week. If it's something I can do with a few compressions fittings then I'll give it a go.

 

[ragj195]

Was the original valve in the CH or HW circuit?

Was it in the flow or return?

Does the bathroom rad heat up when only HW is on?

Turn CH only on and check which valve gets hot first on each rad.

Turn HW only on and repeat the check.

The flow came out of the original boiler then split, with one 22mm going to the cyclinder and the other to the 2 port valve which went on to the CH circuit.

Everything heats up when HW only is on even the the CH valve is definitely close. Although some rads don't get very hot.

I'll do the check and post back. Thx

Hi

Okay I turned on HW only this morning and the bathroom rad gets hot first so it looks like that 15mm goes there. Then it seems the downstairs rads start to slowly warm up. When HW is off and CH on the first rad to got hot is in the 1st floor bedroom directly above the boiler on the ground floor.

 

[D_Hailsham]

Turn CH only on and check which valve gets hot first on each rad.

Turn HW only on and repeat the check.

Okay I turned on HW only this morning and the bathroom rad gets hot first so it looks like that 15mm goes there. Then it seems the downstairs rads start to slowly warm up. When HW is off and CH on the first rad to got hot is in the 1st floor bedroom directly above the boiler on the ground floor.

That's useful, but it doesn't answer my question.

I asked which valve gets hot first (left or right) on each rad:

(a) when HW only is turned on; and
(b) when CH only is turned on.

If it's the same valve in both cases, the motorized valve is letting water through when HW only is on; but if it changes to the other valve, there is a problem with the way the HW cylinder return has been connected.

A pic showing the cylinder and the 15mm pipe to the bathroom rad would be helpful.

 

[ragj195]

Turn CH only on and check which valve gets hot first on each rad.

Turn HW only on and repeat the check.

Okay I turned on HW only this morning and the bathroom rad gets hot first so it looks like that 15mm goes there. Then it seems the downstairs rads start to slowly warm up. When HW is off and CH on the first rad to got hot is in the 1st floor bedroom directly above the boiler on the ground floor.

That's useful, but it doesn't answer my question.

I asked which valve gets hot first (left or right) on each rad:

(a) when HW only is turned on; and
(b) when CH only is turned on.

If it's the same valve in both cases, the motorized valve is letting water through when HW only is on; but if it changes to the other valve, there is a problem with the way the HW cylinder return has been connected.

A pic showing the cylinder and the 15mm pipe to the bathroom rad would be helpful.

Okay got you. I'll try again. the 2 x two port motorised valves have just been fitted on when HW only is on the pipe to the left of the CH valve in the picture doesn't heat up so I don't think it's passing through.

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• ragj195
• 7 Feb 2014
• 1

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• ragj195
• 7 Feb 2014
• 1

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• ragj195
• 7 Feb 2014
• 1

 

[D_Hailsham]

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• ragj195
• 7 Feb 2014
• 1

There are two connections to the side of the cylinder. The higher one will connect to the HW motorized valve. Does the 15mm pipe connect to the pipe coming out of the lower connection?

If so, can you post a pic showing this connection and as much as possible of the pipework connected to the lower connection? I realize this may be a bit difficult.

 

[ragj195]

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• ragj195
• 7 Feb 2014
• 1

There are two connections to the side of the cylinder. The higher one will connect to the HW motorized valve. Does the 15mm pipe connect to the pipe coming out of the lower connection?

If so, can you post a pic showing this connection and as much as possible of the pipework connected to the lower connection? I realize this may be a bit difficult.

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• ragj195
• 7 Feb 2014
• 1

Couldn't get a photo because there is a cabinet on the side but I could get my head/hand round the back enough to work it out and draw this. The 15mm pipe is definitely coming out of the higher one between the motorised valve and the cylinder.

 

[D_Hailsham]

The 15mm pipe is definitely coming out of the higher one between the motorised valve and the cylinder.

That eliminates one possibility - reverse circulation due to the pipe being connected to the cylinder return. But it raises two questions:

1. Is the bathroom rad completely isolated from the rest of the system?

2. Where is the return for the bathroom rad?

I'm thinking that there may be a path from the bathroom rad return to the rest of the system, so you are indirectly getting a reverse circulation situation.

PS Your subject title is wrong. It should read: Getting CH when only HW is on, etc.

 

[doitall]

If it helps the by-pass valve is after the MV.

 

[ragj195]

The 15mm pipe is definitely coming out of the higher one between the motorised valve and the cylinder.

That eliminates one possibility - reverse circulation due to the pipe being connected to the cylinder return. But it raises two questions:

1. Is the bathroom rad completely isolated from the rest of the system?

2. Where is the return for the bathroom rad?

I'm thinking that there may be a path from the bathroom rad return to the rest of the system, so you are indirectly getting a reverse circulation situation.

PS Your subject title is wrong. It should read: Getting CH when only HW is on, etc.

Thx,

The bathroom rad gets hot when only ch is on also but if there is a path from to the rest of the system I guess that would happen also.

I'm going to lift some boards at follow it through.

Regarding the subject, getting ch when hw is on is what needs sorting but I'm pretty sure this flow issue is heating the hw when only ch is on therefore making the cylinder stat and mv irrelevant.