MP valve in mid postion with HW Only on

[daveywavey]

Hi all,

I had my boiler and tank replaced last year but since turning off the central heating this year, we noticed the radiators were still getting hot. I thought it might be the MP valve as when I disconnected the valve electrically - the rads still heated up so the valve was passing.

I just replaced the old Randall wiring centre with a new honeywell style one suitable for the Sundial Y Plan. I removed the appropriate links and connected everything as per colours indicated and double checked with the honeywell wiring diagram.

I currently am only using hot water so have disconnected the existing MP valve electrically and connected a new one electrically but not physically so I can watch the valve move before fitting to ensure its doing what it should - well its not!!!!

- When CH is selected, the valve moves to CH only and stays there regardless of whether the thermostat is activated or not
- When HW is selected, the valve also moves to CH only but when cylinder stat setting is increased - to demand more heat, it switches to the mid position!
- When CH and HW are selected, it sits in the mid position
- When both CH and HW are turned off, the valve goes to CH only - but this is because it always ends in the mid position and is driven further as normal

Pump/boiler start up correctly and cut in and out when the appropriate thermostat is activated

Any help would be really appreciated - stayed up till 2am looking at this yest!!!


Equipment fitted is:

Worcester greenstar ri boiler (1yr old)
Danfoss HSA3 MP Valve (new)
Drayton lifestyle LP522 Pogrammmer (1 yr old
Honywell wiring centre (new)
Honeywell cylinderstat and roomstat (1 yr old)
Grundfoss pump (1 yr old)

 

[doitmyself]

Is the valve the correct way round? Port A to Radiators, Port B to HW cylinder.

Remove the valve actuator (box on top) and check that the spindle rotates easily between the two positions - it will turn about 45 degrees.
If it's at all stiff, use a small amout of WD40 to free it.

Replace actuator

Here is how to test the valve and actuator:

Turn off power when connecting/ disconnecting wires This usually means unplugging the lead or removing the fuse from a spur.
Disconnect the valves Grey, Orange and White wires (make a note of which terminal they are connected to)
Turn CH OFF and HW ON
Turn HW stat up - boiler should light
HW pipe only from valve should get hot
Turn HW stat down - boiler should go out.
This confirms the Call side of the HW stat is working.
Connect the White wire to a permanent supply.
Turn CH ON and room stat up
Turn HW stat up
Boiler should go on
HW and CH pipes from valve should get hot.
Turn HW stat down
Boiler should go out
This confirms if valve is working in mid-position
Turn HW and CH OFF and set CH and HW thermostats to low
Connect grey wire to a permanent supply
Reconnect the orange wire to its correct terminal
Turn CH ON and CH stat up.
Boiler should light and CH pipe get hot
Turn HW ON (leave HW stat low)
Boiler should continue to run and CH pipe get hot.
This confirms if the valve is working in CH only
Reconnect White and Grey wires to the correct terminals.

If it fails any of these test the fault is in the valve actuator.

If it passes the tests, the fault lies elsewhere. Either the programmer or the HW thermostat.