Y Plan central heating

[Paul49]

On the return circuit is it ok to connect the return from the hot water tank and the return from the radiators with a t-connector just before it is connected to the return connection on the boiler?
Thx in advance
Paul

 

[D_Hailsham]

On the return circuit is it ok to connect the return from the hot water tank and the return from the radiators with a t-connector just before it is connected to the return connection on the boiler?

You must make sure you don't have a reverse return. This is where the return from the radiators connects to the main return after the return from the cylinder. A reverse return can cause reverse flow, this will cause the rads to heat up when just the hot water is on.

All the returns from the rad circuits should join the main return and the return from the cylinder should join the main return after any rad returns, i.e nearest the cylinder.

 

[Paul49]

I have attached a image of the new system, is this acceptable or is there a danger of reverse return?
Thx
Paul

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• Paul49
• 23 Apr 2009
• 2

 

[gas4you]

I personally wouldn't pipe it like this due to the risk of reverse flow.

Why have you got to change it from the previous layout

 

[D_Hailsham]

I personally wouldn't pipe it like this due to the risk of reverse flow.

Why would it create any risk?

"Water flowing in the primary hot water circuit should not pass any connections to the space heating circuit on its way to or from the hot water cylinder. This is to avoid reverse circulation faults which are caused by convective flow around the space heating circuit when it is supposed to be switched off."

Both versions met this requirement, so there can be no reverse circulation.

Why have you got to change it from the previous layout

Seconded.

 

[Paul49]

I have to move the boiler and due to the regs have to change it for a condensing boiler (worcester 18 gas) this is wall mounted and to reduce the amount of pipes running up and down the wall I wanted to join the two returns as they enter the boiler.

 

[gas4you]

Both versions met this requirement, so there can be no reverse circulation.

Whilst in theory this seems logical, the fact that the ch return is rising from the HW return, could just possibly start off a gravity reverse circulation, when only HW is selected.

I have had this before and usually the only way to eliminate the risk is to common all the returns before connecting to the main boiler return.

In this case I would leave as is, or make the common return at a high point after making the pipes neater.

 

[D_Hailsham]

Whilst in theory this seems logical, the fact that the ch return is rising from the HW return, could just possibly start off a gravity reverse circulation, when only HW is selected.

I can see what you are getting at; however I was not taking the OPs diagrams as being the literal layout. But if the return does rise from the ground floor and then run under the first floor until it drops down to the boiler, there could be a risk of reverse circulation

In this case I would leave as is, or make the common return at a high point after making the pipes neater.

Agreed. Like this:

Just realized this looks as if the return from the rads is Teeing into the pipe from cylinder to boiler. It should be the other way round, i.e the pipe from cylinder Tees into the pipe from rad to boiler- as in the "before" diagram"

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• D_Hailsham
• 23 Apr 2009
• 3

 

[Paul49]

The return from the cyl drops from the the first floor into the t at the return inlet into the boiler which is situated on the wall, the return from the first floor radiators drop to the ground floor and joins the down stairs radiator returns and that return raises from the ground floor into the t on the wall mounted boiler. As shown

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• Paul49
• 23 Apr 2009
• 2

 

[D_Hailsham]

As shown

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• Paul49
• 23 Apr 2009
• 2

That's a novel arrangement! Can't see any reason why you should get reverse flow.

 

[swbjackson]

Looks to me like an ideal candidate for reverse flow. The return water is likely to flow straight through the tee and into the heating circuit. The hw return needs to enter the branch of a tee not the end.

 

[mogget]

Looks to me like an ideal candidate for reverse flow. The return water is likely to flow straight through the tee and into the heating circuit. The hw return needs to enter the branch of a tee not the end.

How can the water get in to the heating circuit when the 2 or 3 port valve on the other end is closed?

 

[Norcon]

Looks to me like an ideal candidate for reverse flow. The return water is likely to flow straight through the tee and into the heating circuit. The hw return needs to enter the branch of a tee not the end.

How can the water get in to the heating circuit when the 2 or 3 port valve on the other end is closed?

IF you had the CH return on an upper level T'd into the cylinder return before this return enters the primary return then water may reverse flow through an upper rad and then flow normally through a lower floor rad back to the primary return.

 

[mogget]

Yes, I understand this as I had to sort out the same problem in my own house.

Swbjackson was questioning the alignment of the tee, which I think is a red herring.

Provided all the rad returns come together before joining the dhw return, there is no circuit and there can be no circulation IMO.

 

[Paul49]

IF you had the CH return on an upper level T'd into the cylinder return before this return enters the primary return then water may reverse flow through an upper rad and then flow normally through a lower floor rad back to the primary return.

If you read my earlier description you will see I do not have it piped in as you described, the only place the two circuits meet is at the t as shown in the drawing.