Loft boiler gravity feeding

[dave_sch]

I recently had my old open vented kitchen boiler replaced with a loft system boiler. All works fine apart from one issue:

If the 3 port valve is at rest with CH and HW off, ie in the hot water position, the hot water in the indirect cylinder upstairs heats the water in the coil which then gravity feeds backwards up the flow pipe to the boiler and back round. The result is loss of much of my hot water during the course of the time the system is off.

I could cure it by replacing the 3 port valve with 2 x 2 port valves, but that would be fair bit of work and cost. The other idea I thought of was a single check valve between the 3 port valve and the cylinder. Would that work okay, or cause any problems ?

 

[dave_sch]

I recently had my old open vented kitchen boiler replaced with a loft system boiler. All works fine apart from one issue:

If the 3 port valve is at rest with CH and HW off, ie in the hot water position, the hot water in the indirect cylinder upstairs heats the water in the coil which then gravity feeds backwards up the flow pipe to the boiler and back round. The result is loss of much of my hot water during the course of the time the system is off.

I could cure it by replacing the 3 port valve with 2 x 2 port valves, but that would be fair bit of work and cost. The other idea I thought of was a single check valve between the 3 port valve and the cylinder. Would that work okay, or cause any problems ?

Another thought - would an anti gravity loop between the 3 port valve and cylinder do the trick ?

 

[dcawkwell]

If the piping is adjusted to take the the flow pipe of the cylinder down to the bottoms of the cylinder before going up that would cure it.

Alternatively the 3 port valve can be turned around and the open side then
becomes central heating. The two switching wires are wired together
and the 3 port valve becomes a diverter that diverts fully to hot
water when heating the tank when the tank isn't calling the 3 port returns
to central heating position. If you tank is new this will be fine as it
will heat up quickly because when the boiler is heating the hot water
the central heating will be off. But that might only be for 10-15 minutes
at a time when a large quantity of water has been used.
However if the tank is old with a big lazy coil not recommended as it could be heating the hot water for an hour or more.

 

[dave_sch]

If the piping is adjusted to take the the flow pipe of the cylinder down to the bottoms of the cylinder before going up that would cure it.

Alternatively the 3 port valve can be turned around and the open side then
becomes central heating. The two switching wires are wired together
and the 3 port valve becomes a diverter that diverts fully to hot
water when heating the tank when the tank isn't calling the 3 port returns
to central heating position. If you tank is new this will be fine as it
will heat up quickly because when the boiler is heating the hot water
the central heating will be off. But that might only be for 10-15 minutes
at a time when a large quantity of water has been used.
However if the tank is old with a big lazy coil not recommended as it could be heating the hot water for an hour or more.

Thanks dcawkwell, of the 2 options, the first would be easier to do. Just to check though, I assume what you are suggesting is a deep loop with the flow still connected to the top of the coil?

I notice you made no comment about my original suggestion of a NRV. Any reason for not using that as a solution?

 

[dcawkwell]

If the piping is adjusted to take the the flow pipe of the cylinder down to the bottoms of the cylinder before going up that would cure it.

Alternatively the 3 port valve can be turned around and the open side then
becomes central heating. The two switching wires are wired together
and the 3 port valve becomes a diverter that diverts fully to hot
water when heating the tank when the tank isn't calling the 3 port returns
to central heating position. If you tank is new this will be fine as it
will heat up quickly because when the boiler is heating the hot water
the central heating will be off. But that might only be for 10-15 minutes
at a time when a large quantity of water has been used.
However if the tank is old with a big lazy coil not recommended as it could be heating the hot water for an hour or more.

Thanks dcawkwell, of the 2 options, the first would be easier to do. Just to check though, I assume what you are suggesting is a deep loop with the flow still connected to the top of the coil?

I notice you made no comment about my original suggestion of a NRV. Any reason for not using that as a solution?

Yes flow still from to the top of the coil then take it down to
the bottom of the tank or slightly lower if possible then up to the boiler.
You may well need an auto air vent at the top of the flow pipe into the cylinder to clear any air here.
Perhaps best to do it for the flow and return pipes.

 

[holty]

http://www.bes.co.uk/products/098.asp

part no 7463

 

[dave_sch]

http://www.bes.co.uk/products/098.asp

part no 7463

Thanks Holty, not heard of that type before, any reason for using that over a ball type check valve such as part 8150, the latter having the advantage of being a 22mm fitting ?

 

[dave_sch]

If the piping is adjusted to take the the flow pipe of the cylinder down to the bottoms of the cylinder before going up that would cure it.

Alternatively the 3 port valve can be turned around and the open side then
becomes central heating. The two switching wires are wired together
and the 3 port valve becomes a diverter that diverts fully to hot
water when heating the tank when the tank isn't calling the 3 port returns
to central heating position. If you tank is new this will be fine as it
will heat up quickly because when the boiler is heating the hot water
the central heating will be off. But that might only be for 10-15 minutes
at a time when a large quantity of water has been used.
However if the tank is old with a big lazy coil not recommended as it could be heating the hot water for an hour or more.

Thanks dcawkwell, of the 2 options, the first would be easier to do. Just to check though, I assume what you are suggesting is a deep loop with the flow still connected to the top of the coil?

I notice you made no comment about my original suggestion of a NRV. Any reason for not using that as a solution?

Yes flow still from to the top of the coil then take it down to
the bottom of the tank or slightly lower if possible then up to the boiler.
You may well need an auto air vent at the top of the flow pipe into the cylinder to clear any air here.
Perhaps best to do it for the flow and return pipes.

I'd still welcome your view on the use of a single check valve or a swing check valve as Holty suggests, both of which would involve less work and cost and I'm sure would stop the gravity feeding. My only concern is whether either would cause a problem in normal operation, for example whether the flow through the valve would be sufficient, especially in CH and HW mode when pump pressure through the valve would presumably be less.