odd gatevalve in airing cupboard

[ross94]

Hi all, I have a y plan gravity fed heating system, in the airing cupboard there is your normal setup, heating pump 3 port valve ect. However I have noticed this gate valve on the system and have always wondered what it is and what it does. I will describe it best I can without a picture, so here goes, Just after the pump in between the pump and the 3 port valve there is a T joint reduced to 15mm which goes to the gate valve in question then goes to the return pipe.

This valve appears to be only half open, I have left it as it was before. just like to know what it is and what it does?. thanks

 

[Nozzle]

So kind of bypass - if you have the three way valve set to heating only, and the rad stats are satisfied, there might be only one rad (the one with no TRV) with any flow through it. This will overheat your pump, being at or near dead head.

Nozzle

 

[ross94]

I see so its like a bypass valve then, so its there to let the water still circulate round the system after the port valve has shut or all the radiators are shut, or if the pump was to overrun after the boiler switched off it would prevent the pump from burning out or overheating due to the water having nowhere to go.If that makes any sense. is this correct?. thanks

 

[ross94]

so is that what it is for then? ta

 

[Nozzle]

That's my guess, yeh

Nozzle

 

[MANDATE]

Relative has similar system, with one radiator furthest away from boiler not getting hot.
It was easier for water to go back to boiler via by pass valve, rather than radiator.
Problem solved by slightly closing this valve and restricting the flow through it.

 

[stuartR1963]

Hard to tell without pictures,but it does indeed sound like a bypass valve. useful if you have a pump overrun(giving the water somewhere to go to stop the pump burning out or overheating due the water having nowhere to go. or if all radiators were switched off for some reason, it will still allow the water to flow round the system. I believe it is there just to protect the pump. so leave it alone.
It could also be a balancing valve but more likely a bypass. thats my guess

 

[wannocks]

Its also there to protect the boiler to allow some flow even when most of the rad valves are closed.