combi boiler/non-return valves

[davenport.neil]

I am currently re-jigging my central heating layout to accommodate a wet underfloor heating manifold and 2 radiator zones in an S-plan layout. All 3 will have a separate zone valves and the boiler is a combi/direct hot water.

Can anybody advise me if there is a need to fit any non-return valves to prevent any reverse flow and if so where should they be located?

I am assuming that as all zones have zone valves reverse flow is not possible but would appreciate any informed advice.

Also is the boilers built-in auto-bypass valve sufficient for this layout or is a secondary one required?

Thanks in advance

 

[R1CKY]

You don't need non return valves, but you need to consider your return pipework positions to avoid reverse circulation. I'd seperate each zone and pipe the returns as close to the boiler as possible.

A secondary auto bypass won't hurt, boiler bypasses seem to be very small bore and can block up quite easily.

 

[Howsie]

Agree with the secondary bypass. Don't put in non-return vales, why add extra resistance to a circuit? Plumb it properly.

Good luck!

 

[davenport.neil]

You don't need non return valves, but you need to consider your return pipework positions to avoid reverse circulation. I'd seperate each zone and pipe the returns as close to the boiler as possible.

A secondary auto bypass won't hurt, boiler bypasses seem to be very small bore and can block up quite easily.

Thank you for your reply.
Because of space restrictions under the floor near the boiler and a difficulty accommodating all the pipes the flow splits to the 3 seperate zone flows within 500mm of each other and approx 4.5 meters from the boiler in the adjacent room , the returns are similar in reverse. It will be diffult to have this any closer to the boiler.

 

[R1CKY]

They don't necessarily have to be near the boiler, but what you don't want is a return from one zone being tee'd in between returns from other zones. Difficult to explain without drawing a pic.

 

[Howsie]

There is always a way of doing it right rather than bodging it.

 

[davenport.neil]

They don't necessarily have to be near the boiler, but what you don't want is a return from one zone being tee'd in between returns from other zones. Difficult to explain without drawing a pic.

Thank you for this explanation.
So in effect if the underfloor heating manifold return runs straight through (manifold is 12 metres of pipe from boiler) then is there a minimum distance i should have beween the Tees' of the 2 radiators zones onto the main return??
If this is the case what distance is good , 1/2metre , 1 metre, 2 metres ?

 

[Ollieg]

Research "3 tee rule" it explains where to place tees to prevent problems. Honeywell once had a book about it.

 

[AWheating]

sounds like the system will work fine, stick a by pass in and bobs your aunt.