Mid position Valve

[scooby0606]

HI

I have a 3 year old central heating system (yes 1 month past warranty) that I think has an MPV problem. When the heating is on and the water is below temperature it does not divert. If I turn the heating off it diverts straight away (I believe water is default anyway) and I can turn the heating back on and all is fine. However tonight the water was fine but it would not switch to heating until I turned the water off ! I could then turn it all back on and all fine.

Is this likely to be the MPV, if so is it likely to be the entire unit or can I buy a part (I know some parts are available) and therefore not drain down the system. The unit is a Honeywell V4073a1088

Thanks

 

[D_Hailsham]

Mid-position valve operation and fault finding should help you sort it out.

 

[scooby0606]

Thanks for the reply off to get a meter.

I have been trying it again tonight and it seems if the heating is on and water is required it will not divert... nothing happens at all, but if I turn the heating off on the programmer the vallve moves, pumps starts and boiler fires up.... hot water here we come. I turn heating back on and it carries on all fine... unitl the water stops and it then wants to start again later....

 

[D_Hailsham]

what happens if you turn the HW thermostast (on side of cylinder) up?

You need to check the voltage on the valve's grey wire when the fault occurs. It should be 0Vac if CH and HW are both required.

 

[scooby0606]

thanks for the reply. The water thermo was my first thought but then when the heating didnt come on I pretty much elimated it. Also, as I said if I turn the heating off it works (I know the mpv defaults to water) and if the thermo wasnt working I didnt think it would heat at all.

Just got me a meter, now to electrocute myself!

 

[scooby0606]

Just had another look.

Heating on, call for water, mpv makes noise any moves about 1 or 2mm (sounds like more). Turn water off, moves back. Turn heating off, water on, moves about 2,3 way acrross. Is it pheasable its just not moving as much as it thinks it is when water is called for ( heatiing on) ?But when going from just water to heating and water it doesnt travel as far back the other way and works ? (aa bit like a dead spot one side)....

Not good with meter just going to google how to use it !

 

[D_Hailsham]

Heating on, call for water, mpv makes noise any moves about 1 or 2mm (sounds like more). Turn water off, moves back. Turn heating off, water on, moves about 2,3 way across.

The movement of the lever in the slot is not a reliable indicator of the valve position.

1. The lever is not physically attached to the valve, it's free to move in the slot when the valve is held in Mid or CH position
2. The lever only opens the valve to mid-position - it's really there to open the valve when the system is being filled.

When the valve is in HW position, the lever should be hard to move as it is opening to mid/CH position; when in mid/CH position it should be loose.

Is it pheasable (feasible) its just not moving as much as it thinks it is?

The valve could be sticking.

Turn power off
Remove metal cover - 1 screw at end
Undo two screws in diagonally opposite corners
Lift off Actuator
The spindle is now visible.
It should turn easily by hand (less than a quarter turn)

If stiff, lubricate round the seal with silicon lubricant -NOT WD40, which will rot the seal.

Not good with meter just going to google how to use it !

The meter needs to be set to AC volts over 250.

You always measure between the terminal you are checking and Neutral (blue wires). The valve has its own neutral wire, so you can use that.

 

[scooby0606]

Thanks for the advice

Removed the head and the first thing that happened was the acruator moved all they way to the auto position (yes I left it on), never seen it move that far. I turned the spindle and it moved freely but no where near 1/4 turn, more like 1/8. I dont want to try and force it anymore... does this sound far enough, certainly free movement over that 1/8th

 

[scooby0606]

Sorry meant say, so on the meter I need to check the grey by placing one on the blue anbd one on the grey at 250ac

 

[D_Hailsham]

1/8th of a turn is fine. Honeywell say 15 to 20 degrees.

Yes, you measure between grey and blue. It's also worth checking white and blue. You should get the following:

HW only: White 0V; Grey; 0V. (You may get voltages between 50 and 150, but that's OK.)

HW and CH: White 240V; Grey 0V. (Same as above)

CH only: White 240V; Grey 240V.

When CH is satisfied/turned off: White 0V; Grey 240V.

When HW is required: White 0V; Grey 0V

 

[scooby0606]

D_Hailsham - Thanks for your time and advice.

First test I did:


CH only: White 240V; Grey 240V

Second test, added water:

HW and CH: White 240V; Grey 80V

Ill do some more. But could this possibly have an intermittently faulty microswitch, would that reflect in these voltages ?

 

[D_Hailsham]

CH only: White 240V; Grey 240V

That's correct.

Second test, added water:

HW and CH: White 240V; Grey 80V

240V on white is correct. As I said the grey will have a voltage on it, but it's too low to have any effect. If you look at the CH+HW diagram in Mid-position valve operation and fault finding you will see that there is a resistor connecting the orange and white. As the orange is connected to the same terminal as the cylinder stat Call, you will automatically get 240V on the orange and a lower voltage on the grey when HW is called.

Did the boiler work when you did the second test?

If it didn't, check the voltage on the orange/HW stat Call.

 

[scooby0606]

Thanks again.

I observed the water didnt seem to be heating again so re-metered it:

White 0 Grey 250

Turned up cylinder stat, still no change

Turned off heating and voila pump fired, boiler fired and started to heat water

Reading White 0 grey 0

I then turned the CH back on and Im sure it read

White 0 grey 0 still

 

[scooby0606]

Just had a call frpn the mrs, no heating now!!! Consistent with voltage above but stat is calling for heating

 

[scooby0606]

A comprehensive mornings testing.

Got up and observed no hot water so:

Progammer shows heating constant (but up to temperature on stat)
Water constant. Felt pipes around MPV, hot to heating, cool to water cylinder

Voltage at MPV white 0 grey 250

Heating requested by room stat

Voltage at MPV white 250 grey 250

Heating satisfied

Voltage at MPV white 0 grey 250

Turned off heating on programmer (from const to off)

Heard MPV move, boiler fired and pipe to cylinder started to warm

Voltage at MPV white 0 grey 0

Turn heating on at programmer

Heat not called for as stat does not require it

Voltage at MPV white 0 grey 0

Call for heat by turning up stat

voltage at MPV white 0 grey 0

and the rads are cooling

So it seems my system is only capable of doing hot water or rads when the other is switched off on the programmer