Honeywell V4073a hot water priority???

[richig]

Have a question about the Honeywell V073a mid position motorised valve.

My system is vented, fully pumped Y plan with a Potterton Suprima non condensing boiler – small house – 7 single panel rads and 125 litre HW cylinder. All works fine at the moment however…


I noticed that when the CH and HW are on together and there is definitely a call for heat from both, the system seems to give priority to HW. I only found this by doing the following several times…

Cylinder and rads are cold (not used for a few days), turned HW on (normally takes about 40 min to heat fully cold cylinder this time of year), some 10 min later decide to turn CH on. Rads begin to heat slowly. 5 min later turn HW off – there is still call for heat for cylinder as water still cold – boiler goes off (which to me indicates it has only been heating the cylinder despite slight warmth in rads?) then cycles pump and fires again for CH only as HW is now off.

This is not causing any issues and the boiler is serviced yearly but Im just curious – does the v4073a somehow give priority to the HW when there is a call from CH and HW together (this would probably make sense in most circumstances?)

Thanks…

 

[richig]

Should add that after an hour or so the hw and CH both come up to temp and all is fine! Its just during the heating up process that HW seems to have priority?

 

[D_Hailsham]

Cylinder and rads are cold (not used for a few days), turned HW on (normally takes about 40 min to heat fully cold cylinder this time of year), some 10 min later decide to turn CH on. Rads begin to heat slowly. 5 min later turn HW off – there is still call for heat for cylinder as water still cold – boiler goes off (which to me indicates it has only been heating the cylinder despite slight warmth in rads?) then cycles pump and fires again for CH only as HW is now off.

The signal to turn on the boiler, when in HW only or HW+CH modes, comes from the cylinder thermostat. When in CH only mode the signal comes from the orange wire of the motorized valve. The delay between HW+CH and CH only is caused by the time it takes for the valve to move from mid-position to CH only position.

The cylinder will only get priority, in HW+CH mode, if the cylinder has not been balanced by restricting the flow through the cylinder (There is normally a gate valve on the cylinder return which can be used for this.)

Balance the rads first, with HW turned off, then set to CH+HW (both calling for heat) and adjust the gate valve to give the same temperature drop across the cylinder flow and return.

 

[richig]

Thats great - I always wondered what the gate valve in that position was for - Thanks a lot!