Help needed please...CH and HW gone slightly crazy!

[MSP1]

Hi All, hoping somebody could give me some pointers with this problem. Sorry if any of the details below are not relevant, but I figure it best to describe in full what I have tried and noted.

Glowworm Ultracom 24hxi condensing boiler in airing cupboard with HW cylinder
Drayton LP722 control unit
Honeywell 3 way MV
Honeywell cylinder thermostat

Initially, I noticed a couple of downstairs rads were not heating very well recently. Having looked around this forum I decided the system needed balancing. I followed the instructions found in another thread and turned the locks off on the rads, turning them back on a quarter turn each. All upstairs rads continued to work as expected, still not a lot of heat from the rads downstairs.

I noticed that the hot water at the taps was extremely hot and thought maybe the cylinder thermostat was at fault. I don't hear any clicking sound when increasing or decreasing the temp setting on the cylinder.

However, I also discovered that the water was being pumped to both the HW and CH system simultaneously, even if I turned the HW off. This is how it has been for the past week or so. With the HW set to OFF, when the CH is on, the rads heat up ( still a bit dicky in a couple downstairs ) but very hot water is still being sent to the cylinder. All pipes from the 3 way motorised valve are hot constantly.

The MV slider (?) for auto/manual is loose and flappy with no resistance at all. I have just switched off all power to the house and opened the MV. With no power, the slider DOES have resistance and can be pushed to auto or locked to manual. With the power back on it goes loose again. Possibly perfectly normal, I have no idea!

After restoring power to the house I decided to see what would happen if I reversed things on the control unit so that the CH was OFF the HW was on. Cold water then ran through all pipes out of the MV. I have just checked again and the pipes are now hot, but the boiler has not started and the display for the boiler is showing 38c.

So...
With the HW off and CH on, both the rads and water cylinder are heated. HW is extremely hot and seemingly uncontrollable by the cylinder thermostat.
With the CH off and the HW on, cold water was initially running through the MV but this is now hot water, despite the boiler sitting quietly minding it's own business.

I just can't get straight in my mind what may need looking at and in what order. I was going to pop out and get a new honeywell MV, but not sure if I need the motorised section alone or the whole assembly. I thought the floppy lever indicated a fault, but was then surprised when it was stiff without power. This is all sounding like fifty shades of plumbing now!

Any help very gratefully received.

All the best,
Lee.


Update
With the HW on I increased the cylinder thermostat way up, beyond 80c, and the pump and boiler started up AND the MV lever has resistance...can be pushed to the right to manual and moves itself back over to the left.

 

[Agile]

Whilst well written your description is difficult for me to follow, probably mostly because you did not find out more about what you are doing first.

The motor valve is like a relay and turns the boiler and pump on when its open.

The lever has resistance and can be opened manually when its not powered ( although NOT to the point where the relay contact makes if its latched in the open position ).

When it is powered the lever feels floppy because the motor has already moved it to the open position.

You may need to check the cylinder stat is switching correctly. This needs a test meter!

Tony

 

[stem]

I think you have identified what's happening. When the hot water cylinder is at the temperature set on the cylinder thermostat, if the central heating is also calling for heat, the motorised valve should wind fully across and close off the hot water port. This is not happening, as water continues to circulate around the hot water circuit, less water is available for the radiators, which is why the downstairs rads are cooler.

There could be several faults that may cause this. First of all there is a grey wire from the motorised valve, this should be live when hot water is not required. If you have a multimeter and are able to use it safely, then this is the one to check first.

Make sure that hot water and central heating are both selected 'on' at the programmer. Then turn the cylinder thermostat down (if the hot water cylinder is already hot then you may not hear it click 'off') the grey wire to the motorised valve should now be live. If it's not, then there is a fault with the cylinder thermostat or it's associated wiring, if it is live then the motorised valve is not closing on receipt of the signal and is faulty.

Whilst you've got the wiring exposed, it might be worth just checking to see the neutral is present at the motorised valve. I think it is, as you say the valve motor is operating to an extent hence the 'floppy lever'

Excellent description BTW, especially for a first time post. It makes a change from the usual two liner.

 

[MSP1]

Thanks both for the quick response, this gives me something to work on, thank you.

Tony, agreed, lack of knowledge on my part. In my defence I didn't anticipate becoming a makeshift plumber, but it became a case of needs must after not receiving replies from the two plumbers I left messages with to contact me.

 

[Agile]

You really need a heating or boiler engineer rather than a general plumber who will probably not be experienced in fault finding on these systems.

Even many for install boilers become lost when faced with any electrical problem!

Tony