The final return tee: always the immersion cylinder return, but is it a standard?

timetraveltim · Oct 23, 2018

Hi,

Long story short: my boiler (gas, conventional, vented, three port system) has been moved from one side of the house to the other.

Previously the immersion cylinder return was the final tee before reaching the boiler, and all worked fine.

Now the immersion cylinder return is a few tees before the boiler, and I'm experiencing many of the radiators coming on when only hot water is called for. The heating side of the 3 port remains cool, so I believe that this is reverse flow caused by the the freedom of water to go into radiators closer to the boiler return.

All of the materials I can find say that the immersion cylinder return must be the final tee before the boiler - and it makes perfect sense (the water can therefore only return to the boiler because the other direction is ultimately blocked by the 3 port valve being closed).

Anyhow, is there a standard attached to this principle that I can refer to, please?

Thanks

Chalked · Oct 23, 2018

It’s a misunderstanding to think a cylinder return should be the last tee on the return.
In fact it doesn’t matter. All that does matter, is that all returns on the radiator circuit are teed in a common return, before joining the primary return.

fixitflav · Oct 23, 2018

Chalked said:
It’s a misunderstanding to think a cylinder return should be the last tee on the return.
In fact it doesn’t matter. All that does matter, is that all returns on the radiator circuit are teed in a common return, before joining the primary return.

I don't see what you mean there. If "all returns on the radiator circuit are teed in a common return, before joining the primary return" that is the same as all heating returns being commoned before joining the cylinder return. And it's essential, to avoid the problem the OP is seeing.

AWheating · Oct 23, 2018

Google the three tee rule.

Originally it was vent/feed ,cylinder and heating then when system design changed it may have been bypass, cylinder , heating.

Not sure if there's have ever been a British standard for it. It would come under general design practices.

chris watkins · Oct 23, 2018

Sounds very much like the work was completed by someone who didn't know what they were doing !!
Non-return valve is likely to be your only hope now.
but for god sake don't use the spring loaded type.

Sharp Point · Oct 23, 2018

chris watkins said:
Sounds very much like the work was completed by someone who didn't know what they were doing !!
Non-return valve is likely to be your only hope now.
but for god sake don't use the spring loaded type.

Or just repipe it, remember you’re not a fan of gadgets that bodge things

timetraveltim · Oct 23, 2018

Thanks very much for the reply. Here's a grainy shot of the problem:

A is where the original final return for the boiler was.
B is a return from some of the the upstairs radiators
C is the return from the immersion cylinder
D is the return from all other radiators.

The problem is that A has now been capped, and the boiler return is now at the far end of D, beyond various radiator return tees.

Advice very much appreciated, thank you

timetraveltim · Oct 23, 2018

Chalked said:
It’s a misunderstanding to think a cylinder return should be the last tee on the return.
In fact it doesn’t matter. All that does matter, is that all returns on the radiator circuit are teed in a common return, before joining the primary return.

Thanks very much. Radiator tees exist on both sides of the immersion cylinder return, so not in a common return at all. (Apologies - I'm a newbie!)

timetraveltim · Oct 23, 2018

General design practices sound good - I'll search it out. The Three Tee Rule makes sense, thank you. I just need to create a cohesive argument to get the person who did the work to fix it, hence the wish to get something official. Much appreciated!

The final return tee: always the immersion cylinder return, but is it a standard?

timetraveltim

Chalked

fixitflav

AWheating

chris watkins

Sharp Point

timetraveltim

timetraveltim

timetraveltim

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