Adding a secondary return to a system

[mutley racers]

Hi, what do people a think is the best way to add a secondary return to an unvented cylinder install.

The scenario is I am quoting to replace a gravity system with an unvented. The bathroom furthest away takes around 2 minutes to get hot water. The problem is all the floors are glued and screwed tongue and groove chipboard so not easy to take up and run the return.

Cheers

 

[Scott_D]

Up into the loft and back?

 

[mutley racers]

Up into the loft and back?

Do you mean run new supplies into the bathroom from the loft?

 

[Scott_D]

Do you mean run new supplies into the bathroom from the loft?

Just tee into the hot and run a return back to the cylinder

 

[mutley racers]

Just tee into the hot and run a return back to the cylinder

Tough unless I start removing tiles. Guess that will be easier than the floor though. Thanks Scott

 

[Scott_D]

10mm copper is big enough

 

[EvilDrPorkChop]

Is there any plastic on the system? If there is it's a big no no.

Also you'll probably find that under pressure the hot water will come a lot quicker anyway.

 

[Aire]

Is there any plastic on the system? If there is it's a big no no.

Also you'll probably find that under pressure the hot water will come a lot quicker anyway.

Is there an issue with secondary returns and plastic?

 

[Scott_D]

Is there an issue with secondary returns and plastic?

Manufacturers say it can’t be used

 

[Aire]

Manufacturers say it can’t be used

Really? We've just done a new build with about 90% plastic. It was installed with a secondary return. Which manufacturer, the pump or cylinder manufacturer?

 

[EvilDrPorkChop]

Really? We've just done a new build with about 90% plastic. It was installed with a secondary return. Which manufacturer, the pump or cylinder manufacturer?

Owch, the get the towels ready.

All the plastic manufactures. Circulating return has to be copper then the branches have to be 1 metre in copper then can go to plastic.

 

[Scott_D]

Really? We've just done a new build with about 90% plastic. It was installed with a secondary return. Which manufacturer, the pump or cylinder manufacturer?

The pipe manufacturer.
I worked for a company that did the hot water in plastic and the return in copper. They seemed to think that was ok.

 

[Aire]

Oh dear . Well you learn something new. Do we know the reason behind this? Surely it can't be because of heat.

 

[Scott_D]

Oh dear . Well you learn something new. Do we know the reason behind this? Surely it can't be because of heat.

It’s not suitable for constant high temperatures

 

[Aire]

It’s not suitable for constant high temperatures

But central heating runs hotter than a hot water return and there's no issues with that.

 

[Scott_D]

But central heating runs hotter than a hot water return and there's no issues with that.

If the CH was on constantly for a few days the house would be pretty warm and the boiler will be on/off cycling

 

[Aire]

If the CH was on constantly for a few days the house would be pretty warm and the boiler will be on/off cycling

On that assumption then, a timer fitted to the hot return will solve the problem.

I've read another post on another forum about this and some quoted text basically says that the pipe is manufactured to whichever British standard, but because that British standard doesn't cover secondary returns, they say their pipe isn't suitable.

 

[Scott_D]

On that assumption then, a timer fitted to the hot return will solve the problem.

I've read another post on another forum about this and some quoted text basically says that the pipe is manufactured to whichever British standard, but because that British standard doesn't cover secondary returns, they say their pipe isn't suitable.

Yeah
Unless someone sets it to constant. It would be your choice, but the manufacturers say not suitable so no warranty etc

 

[Aire]

Yeah
Unless someone sets it to constant. It would be your choice, but the manufacturers say not suitable so no warranty etc

Well we're not going to pull the pipe out now, the house has just been finished. It sounds more of a get out clause from the manufactures than an actual problem with doing it. Has anyone had a failed pipe due to it been fitted on a secondary return?
Really by them saying the return has to be copper but the main pipe can be plastic, they are basically saying it's fine.

 

[mutley racers]

Interesting guys. Good to know. These houses are all copper. No plastic.

 

[Scott_D]

Well we're not going to pull the pipe out now, the house has just been finished. It sounds more of a get out clause from the manufactures than an actual problem with doing it. Has anyone had a failed pipe due to it been fitted on a secondary return?
Really by them saying the return has to be copper but the main pipe can be plastic, they are basically saying it's fine.

A company I worked for said that it was fine to do it that way.
I don’t think it is as it’s all under the same pressure and at the same temp

 

[Aire]

A company I worked for said that it was fine to do it that way.
I don’t think it is as it’s all under the same pressure and at the same temp

Oh it wasn't hep that said that. I think I'll give them an email just to clarify if it's really an issue or not, obviously as you say the guarantee will be void but I can live with that. I'll know for future installs though

 

[Scott_D]

It’s a pretty clear no

 

[Aire]

It’s a pretty clear no
View attachment 38467

Yes but that only states that their pipe is manufactured to hot water systems covered under BS7291 which doesn't cover secondary returns. It just basically says they havent tested their pipe on secondary return systems. It also says continuously operated hot water systems. Add a timer and it isn't continually operated, also at some point the stored hot water will deplete. Still just seems like a get out clause. I'm not arguing with you by the way, just a debate that's all.

 

[Scott_D]

Yes but that only states that their pipe is manufactured to hot water systems covered under BS7291 which doesn't cover secondary returns. It just basically says they havent tested their pipe on secondary return systems. It also says continuously operated hot water systems. Add a timer and it isn't continually operated, also at some point the stored hot water will deplete. Still just seems like a get out clause. I'm not arguing with you by the way, just a debate that's all.

They must have a reason to say must not be used.
If you think of worst case scenario
Cylinder immersions set to 70
On 24/7 and return pump on constant

The plastic pipes goes a bit floppy and you could have a fitting blow off.

At least most CH systems are sealed so you would only get a few buckets of water.

 

[Aire]

They must have a reason to say must not be used.
If you think of worst case scenario
Cylinder immersions set to 70
On 24/7 and return pump on constant

The plastic pipes goes a bit floppy and you could have a fitting blow off.

At least most CH systems are sealed so you would only get a few buckets of water.

Only reason I can see is the British standard thing. If it had been tested and found the pipe fails under a secondary return system then surely they would state that.
They say their pipe will function correctly for 50 years at 90°c temperature and at 6bar so even in the most extreme cases of an unvented system breakdown, the pipe should be fine.

 

[EvilDrPorkChop]

I believe it's something to do with the heat and it being oxygenated water. In a sealed system the water isn't fresh.

However I've never come across a proper answer to the question.

I only really found out about it when a few years ago a plumber I know had an issue with Polypipe fittings failing due to the circulating return. The fittings were just crumbling to bits, it was the second time in this house they'd had a flood because of the issue.

However as the system was fitted before 2007 the plastic manufactures hadn't realised by that point the circulating returns caused an issue. So they honoured the warranty, however I think since 2008 they've strictly stated that they cannot be used for cirulating returns.

 

[Aire]

I believe it's something to do with the heat and it being oxygenated water. In a sealed system the water isn't fresh.

However I've never come across a proper answer to the question.

I only really found out about it when a few years ago a plumber I know had an issue with Polypipe fittings failing due to the circulating return. The fittings were just crumbling to bits, it was the second time in this house they'd had a flood because of the issue.

However as the system was fitted before 2007 the plastic manufactures hadn't realised by that point the circulating returns caused an issue. So they honoured the warranty, however I think since 2008 they've strictly stated that they cannot be used for cirulating returns.

Crumbling fittings sounds extreme, I wonder how many systems there are out there that are ran in plastic. I know my bosses house has plastic secondarys which have been fine for 10+ years.

 

[Jim Goodenough]

This is a very interesting topic, does it have anything to do whether you are in a soft or hard water area?

 

[EvilDrPorkChop]

This is a very interesting topic, does it have anything to do whether you are in a soft or hard water area?

No.