Whats this valve for?

[plotnine]

I have a simple fully pumped CH and HW system. The flow from the pump connects the two zone valves from a tee connection. The controller allows for separate function of the zone valves so it is possible to have just hot water, just central heating, or both depending on timer settings.

I also have one gate valve whichh I can’t not see the reason for.

After the pump and before the tee to the zone valves there is a tee. This feeds to a gate valve that is just cracked open, the outlet connects to the downstream side of the HW water zone valve via another tee.

This valve is allowing the hot water to bypass the HW zone valve even when only CH is called for.

Any ideas why the corgie plumber who installed the system would have fitted it? Is it really necessary and how can I regulate the setting to prevent hot water heating when I don’t want it.


plotnine

[plotnine]

Thanks AJS your comments make a lot of sense. The installation was carried out in the early 90's , recently i had to replace the controller and i fitted a Drayton Tempus 6 which gave me the ability have the heating on without hotwater for the first time, the old controller gave HW or HW and CH but not just CH on its own.

I am an OAP and becoming concerned about gas prices it seemed a good move. I took the oppertunity to put a remote digital thermometer on the tank with a read out on the kitchen. You can guess my comment when i called for CH only and found the Hotwater cylinder was getting as well althought the zone valve was off.

This started the hunt for the fault and i am sure you are right, the gate valve is the wrong valve plumbed in the wrong place. I looked at the Potterton leaflet and it shows a bypass valve but connected into the retun line to the boiler as you said.

Thanks for the info

David

[plotnine]

I started the boiler from cold having selected CH only. I checked the HW Honeywell zone valve was closed by using the manual lever on the valve.

As I said earlier the "gate valve" is plumbed o that it can bypass the HW zone valve.

The line with these two valves in is physically higher than the pump line so if convection can occur it will. I checked the pipe temp by hand. The inlet side of the HW zone valve remained cool indicating that the valve was blocking flow ie shut but the downstream side got hot as did the interconnecting pipe which contains the gate valve. The gate valve is 1/2 turn from closed.

This indicates to me that the gate valve is passing flow to the heating coil in the cylinder thus creating a full circuit.

I then manually opened the HW zone valve, the pump flow noise changed a bit and the inlet side of the zone valve got as hot as the outlet as one would expect when the valve was opened.

The gate valve is so clagged up, it even has a small drip from the spindle that i doubt if it is possible to shut it fully to test the theory that its this valve which is wrong and also in the wrong place as you suggest.