Y plan bypass valve

[ross94]

Hi, after much trial and error and have finally managed to balance my heating system( usual story upstairs boiling downstairs Luke warm at best) they all heat up fairly evenly now and all get very hot after turning all their locksheilds a quarter turn. One thing i am curious about is the bypass gate valve, its located between the pump and 3 port valve,I am just wondering if it is safe to turn this off?all my radiators have trvs with the exception of the bathroom,en suite and lounge, i understand the 3 port will always allow a flow whether it be a, b or mid position. The valve is currently open about half way and i am just wondering if i need it? The boiler i have is a Worcester 18ri condensing boiler ( old boiler was an ideal classic) overall the system is 20 years old.
Thanks

 

[flameport]

Bypass not required provided at least one radiator is permanently open.

 

[ianmcd]

depends if the one radiator without a TRV and pipework has enough of a heat dump requirement for the min output of your boiler

 

[bernardgreen]

has enough of a heat dump requirement for the min output of your boiler

Would the boiler still be firing after the control system had shut down the radiators and/or cylinder(s) that had been calling for heat ? I was led to believe the by pass was only required to remove the residual heat from the boiler.

 

[CBW]

Would the boiler still be firing after the control system had shut down the radiators and/or cylinder(s) that had been calling for heat ? I was led to believe the by pass was only required to remove the residual heat from the boiler.

No, but pump still over runs, still circulating the heat.

 

[ross94]

Hi, i understand the bypass has been installed a reason and the plumbers probably knew that the 3 port valve would allow a flow, exactly what this valve is for specifically i do not know for sure but i have a few ideas correct me if im wrong, 1: it was fitted in case all radiators had trvs 3 of mine don't. 2: possibly for balancing purposes, 3: maybe to maintain the return temperature on the boiler (if the boiler return pipe temperature is too low maybe it won't work properly/efficiently?
My understandings may be wrong, what is the worst that can happen if this valve is left closed? The boiler i have is Worcester 18kw ri fitted about 5 years ago the old boiler was an ideal classic, the system has 10 radiator and its a gravity pumped system which is 20 years old nothing on the system has been changed besides the boiler.
Thanks

 

[ross94]

To be very clear this is the gate valve i am talking about just after the pump and before the 3 port valve
Cheers

 

[ianmcd]

Would the boiler still be firing after the control system had shut down the radiators and/or cylinder(s) that had been calling for heat ? I was led to believe the by pass was only required to remove the residual heat from the boiler.

Standard TRVs have no electrical intorlock with the boiler so it will keep attempting to fire if the programmer and room thermostats are both calling for heat

 

[bernardgreen]

Standard TRVs have no electrical intorlock with the boiler so it will keep attempting to fire if the programmer and room thermostats are both calling for heat

OK so the boiler can be firing when there is no need for more heating in the building, so the by-pass ( pipework and radiators without TRVs ) will still be putting heat in the building even though it is not required.

No, but pump still over runs, still circulating the heat.

As I learn from Ian a "modern" heating system with TRVs on radiators can keep the boiler firing even though the building is warm enough and needs no further heating.

 

[fixitflav]

depends if the one radiator without a TRV and pipework has enough of a heat dump requirement for the min output of your boiler

I don't think that's an issue. The boiler can still cycle on its control-stat. I have a W-plan system with 15kW non-modulating boiler, no bypass. It's an oldish HW cylinder and I imagine the coil is well furred-up, estimated heat transfer 3kW. When HW is calling the boiler cycles on/off 6-7 times before the cylinder stat is satisfied. Works fine.

 

[fixitflav]

OK so the boiler can be firing when there is no need for more heating in the building, so the by-pass ( pipework and radiators without TRVs ) will still be putting heat in the building even though it is not required.

I don't get that. If no heat is required no stat should be calling and the boiler should not fire.

a "modern" heating system with TRVs on radiators can keep the a boiler firing even though the building is warm enough and needs no further heating.

If so there's something wrong with the controls. Why would anybody want to burn gas if the building is warm enough?

 

[bernardgreen]

I don't get that. If no heat is required no stat should be calling and the boiler should not fire.

I can see it happening when the TRVs on the radiators are warm enough to close but the air temperature around the thermostat(s) is still below the set point(s) of the thermostat(s).

 

[fixitflav]

I can see it happening when the TRVs on the radiators are warm enough to close but the air temperature around the thermostat(s) is still below the set point(s) of the thermostat(s).

But there should be no room-stat in a room with a TRV. If the room-stat is in a different room that's fine, that's how it's meant to work. The TRVs limit the temperature in their room, the room-stat the overall system (as I'm sure you know)

 

[ianmcd]

I don't get that. If no heat is required no stat should be calling and the boiler should not fire.


If so there's something wrong with the controls. Why would anybody want to burn gas if the building is warm enough?

Nothing is wrong it is how older systems worked, you can get systems now where the TRVs are electrically interlocked with the boiler

 

[bernardgreen]

the room-stat the overall system (as I'm sure you know)

Yes I do know that, but if the room thermostat is calling for heat ( doors and windows open ) and the only radiator that is open is in that room then the radiator ( and bypass valve if fitted ) have to be able to dissipate at least the minimum ( modulated ) output from the boiler to prevent the boiler from cycling.

Of course if boiler's maximum output can be dissipated by that one radiator ( and bypass valve if fitted ) then the boiler will not need to cycle