Y Plan??

[Steve200]

Hi, I'm hoping someone can tell me what the 2 motorised valves are doing in my pumped heating/hot water system. The 3 way valve is not the original and is a V4073A which I understand controls both heating and hot water in a Y plan. However, there is also a second valve controlling hot water on the inlet to the hot water cylinder. It's a V4043H which is normally closed and opens when the cylinder thermostat calls for heat.
The system works fine, other than a bit of noise when water is passing through the ABV on pump overun after the boiler cuts out after heating the hot water. The noise goes when I manually open the V4043H and I wondered if I could simply keep it open manually if the system is already fully controlled by the V4073A?
I'd appreciate any advice as I'm confused!
Thanks
Steve

 

[cross thread]

Zone valve is probably the safety valve for a unvented cylinder.

 

[45yearsagasman]

As above. Maybe post a pic of your cylinder and surrounding pipework etc?

 

[Steve200]

Thanks for your replies. I've done my best with a photo but it's all a bit tight! You may be able to see the hot water primary feed coming off the back of the 3 way valve, then looping back then down into the extra V4043H valve before continuing down and left into the cylinder.
I've tried running the system with the V4043H held open and everything seems to work OK. Could it be just duplicating the hot water function on the 3 way valve and would it be OK to just keep it manually open?
The cylinder is unvented and has a separate pressure release valve. If it is a safety valve, could you explain its function?
Really appreciate your help in understanding the system.
Steve

 

[cross thread]

It’s wired into a over heat to stop the source of heat .safety control

 

[Steve200]

That's great - fully understood. I'll leave it to do its job.
Many thanks

 

[Johntheo5]

Its interesting to hear that the 2 port is wired to a overheat, I would also think that the (main?) reason is that a mid position valve can stay in the HW position (last port of call) or fail to its default of HW position.

 

[Madrab]

Yep, in a Y Plan, as the 3 port doesn't have a fail safe to shut down the HW port then the 2 port valve is wired into the high limit side of the cylinder stat as a fail safe, if say the boiler went into a runaway overheat.

 

[fixitflav]

Yep, in a Y Plan, as the 3 port doesn't have a fail safe to shut down the HW port then the 2 port valve is wired into the high limit side of the cylinder stat as a fail safe, if say the boiler went into a runaway overheat.

But shouldn't the 2-port valve close only in an upset (over-temperature) condition, not every time the cylinder stat is satisfied?

 

[Johntheo5]

I didn't realize it was wired via a overtemp, the only one I've seen certainly opened/closed via the progammer/cylinder stat like a S plan which has no overtemp as the 2 port is a (NC) fail save close valve but one picture is worth a thousand words.

Y Plan Heating with Unvented Cylinder and 2 Port Valve

Wiring for a 2 port valve and high limit thermostat when installing an unvented hot water cylinder on a Y plan heating system

flameport.com

 

[fixitflav]

I didn't realize it was wired via a overtemp, the only one I've seen certainly opened/closed via the progammer/cylinder stat like a S plan which has no overtemp as the 2 port is a (NC) fail save close valve but one picture is worth a thousand words.

Y Plan Heating with Unvented Cylinder and 2 Port Valve

Wiring for a 2 port valve and high limit thermostat when installing an unvented hot water cylinder on a Y plan heating system

flameport.com

If that's a reply to my #9, I didn't mean it was wired via a overtemp, just asking the question. If so, and the overtemp wasn't reached (as it wouldn't in normal operation) that would solve the OP's problem. But it would need an additional temperature switch point.

 

[Johntheo5]

Not a repy to yours but it looks like the 2 port auxiliary (end) switch that switches the boiler on/off and as the cylinder control & o/heat stats are wired in series then either one will stop the boiler?, so the control stat is normally switching the 2 port but the regulations now require the extra protection of a o/heat stat, surprising they don't demand it for a vented cylinder as its "only" protection is a vent pipe, a unvented cylinder has three layers of protection, venting at 95C combined with a PRV and generally a expansion valve set lower than the cylinder PRV.

 

[fixitflav]

It’s wired into a over heat to stop the source of heat .safety control

Does that mean there's a cylinder stat temperature switch to stop the boiler, and also a over heat switch to close the 2-port valve? (the over heat point only being reached in an upset condition) In that case the valve doesn't close in normal operation, so wouldn't give the OP's symptoms.

 

[Johntheo5]

The way it works IMO is that the cylinder control stat when satisfied opens and deenergises the 2 port valve, the 2 port valve auxiliary (end) switch then opens and stops the boiler, this is the way that the ops works, as a added layer of protection a NC switch, wired in series with the control stat which opens when/if the o/temp stat operates and the 2 port valve closes, its same auxiliary switch will then open and stops the boiler.

 

[Madrab]

In a Y plan the 2 port valve works in tandem with the 3 port. Usually there is a high limit stat alongside the cylinder stat and they are wired in series. The 2 port valve works as normal and when the HW is satisfied via the cylinder stats, the 2 port closes and stops sending it's SL. It is there as a fail safe though, so if the HL or cylinder stat cuts the power the 2 port closes regardless, just as it would in an S plan