Conventional Central Heating Mystery Pipe?

[Paul95]

Hi, first time i have posted so hope i have done this the right way!

I have had a few problems with my conventional central heating system since I moved into the house. I am trying to get my head round how it all should work. The only thing I can not understand is a small 10mm pipe which is about 50cm long with a manual isolation valve on it in the airing cupboard which has got me baffled. This is not shown on most diagrams I have looked at on the internet and the ones that do don’t explain what it is for.

The pipe branches off the pipe which is between the pump and diverter control valve and connects to the pipe coming from the bottom of the hot water tank which i think goes back to the boiler.

Does anyone know what this is for and if this should be normally closed or open?

Thanks

 

[D_Hailsham]

It sounds like a bypass valve between flow and return. Some boilers need them.

The pipe entering the pump is the flow circuit from the boiler; the pipe out of the bottom of the cylinder connects to the return back to the boiler.

The valve on the bypass will have been set by the installer, so don't touch it.

 

[OwainDIYer]

Another possibility is that it joins the Cold In at the bottom of the cylinder to the hot taps.

When the cold mains off, the valve is opened, and the cold taps opened, the cylinder will empty to cold inlet level.

With the valve closed (or without that piece of pipe), opening the hot tap will only drain down the cylinder to the hot outlet level near the top.

Being able to drain down the cylinder is useful if you need to change a low side mounted immersion heater.

 

[Armo74]

A picture would be useful for a more accurate answer.

 

[Whitespirit66]

Another possibility is that it joins the Cold In at the bottom of the cylinder to the hot taps.

When the cold mains off, the valve is opened, and the cold taps opened, the cylinder will empty to cold inlet level.

With the valve closed (or without that piece of pipe), opening the hot tap will only drain down the cylinder to the hot outlet level near the top.

Being able to drain down the cylinder is useful if you need to change a low side mounted immersion heater.

Untitled

• Whitespirit66
• 31 Jan 2014
• 1

 

[Blagard]

Another possibility is that it joins the Cold In at the bottom of the cylinder to the hot taps.

When the cold mains off, the valve is opened, and the cold taps opened, the cylinder will empty to cold inlet level.

With the valve closed (or without that piece of pipe), opening the hot tap will only drain down the cylinder to the hot outlet level near the top.

Being able to drain down the cylinder is useful if you need to change a low side mounted immersion heater.

I would love to know if you would plumb in like that.

 

[GasCareHeating]

Yeah, defo sounds like a by-pass but no sure why the plumber did it in 10mm pipe, maybe he had run out of other pipe.

 

[Charnwood]

Yeah, defo sounds like a by-pass but no sure why the FREE ADVERTISING - FIRST EVER POST. Tut tut did it in 10mm pipe, maybe he had run out of other pipe.

 

[OwainDIYer]

Another possibility is that it joins the Cold In at the bottom of the cylinder to the hot taps.

When the cold mains off, the valve is opened, and the cold taps opened, the cylinder will empty to cold inlet level.

With the valve closed (or without that piece of pipe), opening the hot tap will only drain down the cylinder to the hot outlet level near the top.

Being able to drain down the cylinder is useful if you need to change a low side mounted immersion heater.

I would love to know if you would plumb in like that.

Well I wouldn't, personally, but it's the only explanation for the bit of small pipe I've got on my cylinder.

It's not a bypass as I don't have a boiler.

 

[Onetap]

Yeah, defo sounds like a by-pass but no sure why the (www.gascare-swansea.co.uk) plumber did it in 10mm pipe, maybe he had run out of other pipe.

Probably because, if it's a by-pass, it is a direct connection between flow and return, there will be a large differential pressure across it and the smaller pipe will provide a greater restriction and make the by-pass flow rate easier to regulate.

Imagine a tradesman not knowing that!
Are you a (www.gascare-swansea.co.uk) plumber?

 

[Blagard]

Well I wouldn't, personally, but it's the only explanation for the bit of small pipe I've got on my cylinder.

It's not a bypass as I don't have a boiler.

If I put a cylinder in it may have a short bit of 15mm tee'd into the cold feed at the bottom, but only when I need to bring it around the cylinder to fit the drain cock where it can actually be used.

You could connect it to a low hot water supply pipe (via a valve) to drain off to a lower hot tap. But you should not connect to the cold main as that is potable supply you are putting it into.

 

[Paul95]

It sounds like a bypass valve between flow and return. Some boilers need them.

The pipe entering the pump is the flow circuit from the boiler; the pipe out of the bottom of the cylinder connects to the return back to the boiler.

The valve on the bypass will have been set by the installer, so don't touch it.

Wow can't believe how many people replied so quickly, much appreciated, i think next time i will try and add a picture/photo with a post.

D_Hailsham, thanks, yes it sounds like it is a bypass, i was wondering that over time the valve may have been turned different to its original position, the valve has a small red wheel handle and it is currently turned fully open. Do you know the reason for this bypass? What would happen if it was closed? Is it normally at a midway position specifically set originally when setting up the system?
The heating is doing strange things and i just wanted to rule this bit of pipe out as being a problem.

 

[gigz]

Do you have a three port valve or two 2 port valves ?

 

[Paul95]

A picture would be useful for a more accurate answer.

i have tried to add a photo, not sure if i have done it the correct way, i clicked upload picture, then created an album called heating and added a photo to it, let me know if you can see it and that i added it the correct way.
I have highlighted the pipe in question and the manual valve, hopefully you can make out the pipework, difficult getting a good angle.

 

[Paul95]

Do you have a three port valve or two 2 port valves ?

3 port valve