Nest 3rd gen - hot water issue

[ericmark]

This may not help you, but I have problems with daughters first house with 3 port valve.

The problem was my diagram of what was inside a 3 port valve was wrong, so my logic was wrong. The problem was diodes and resistors inside the valves give misleading readings.

The problem turned out to be a micro switch inside the valve had stuck, but it took a long time to find.

What had happened was previous owners had latched the bleed lever on the three port valve which kept the heating working, and only when the leaver was knocked snatching it was it noted there was a fault.

I would suggest latch the bleed lever and see what happens.

 

[vikdab]

The problem with the old one was that the heating would remain on at night even though it was off in app (so same problem) but now it is happening ALL the time. I have had 2 boiler engineers but like you say I need an electrician with knowledge of boilers.

From reading elsewhere it looks like faulty micrswitch (unlikely both old and new valves have this) or a fault with boiler.
I will try to get an electrician and also call Viessmann to ask if the 50v might be causing the boiler to remain on

Thanks for your help

 

[muffking]

ok, just thought it was worth checking to see if it was any better with the old valve head back on in case it confirmed an issue with the new heads.

With regards to the low voltages on Grey and White depending on the mode. It's enough to turn some boilers on, but neither of those go to the boiler switched live as the grey is HW satisfied and the white is the call for central heating.

Just another minor check. The red wire you mentioned on the valve head, can you confirm if it's actually an orange wire and what the voltage reading is in all 4 states as that's the wire which goes straight to the boiler switch live to fire it up for heating and/or hot water.
Previously you had it down as:-
Both off = no volts
Heating only = Red live
HW only = Red live
Both on = Red live

 

[vikdab]

hi

The wire is orange indeed. The two oranges from the 2 valves connected to black (switched live?) coming from boiler.

It is same as before
Both off = no volts
Heating only = Red live
HW only = Red live
Both on = Red live

This I believe is correct.

The interesting bit is following. When I turn heating off the voltage in the orange wire drops to 57 but boiler keeps running. The valve lever is also loose . I thought the boiler should stop and the valve spring should come in play. In this rogue state white has 57 and grey 240 - is that valve held in last port of call hence lever doesn't move?

At this point I was wondering as to why the the wrong actuator was able to switch CH off so I connected it back on. When Ch is switched off the white wire has zero V.

I think the boiler stays on with 57V - boiler (relay?) fault?

 

[muffking]

hi

The wire is orange indeed. The two oranges from the 2 valves connected to black (switched live?) coming from boiler.

It is same as before
Both off = no volts
Heating only = Red live
HW only = Red live
Both on = Red live

This I believe is correct.

Yes, looks ok to me too.

The interesting bit is following. When I turn heating off the voltage in the orange wire drops to 57 but boiler keeps running. The valve lever is also loose . I thought the boiler should stop and the valve spring should come in play. In this rogue state white has 57 and grey 240 - is that valve held in last port of call hence lever doesn't move?

At this point I was wondering as to why the the wrong actuator was able to switch CH off so I connected it back on. When Ch is switched off the white wire has zero V.

I think the boiler stays on with 57V - boiler (relay?) fault?

I'd say that shows that 57v to the boiler Switched Live is enough to fire the boiler, but you should have zero volts to the boiler Switched Live when you turn hot water and heating off.
The lever doesn't always move, but the fact that you have 240v on the grey wire when you turned the heating off shows the the valve should be staying on the last port of call i.e. heating & hot water off. You should therefore get zero volts on the orange wire (same as the boiler Switched Live) so the boiler doesn't fire up.

I'm still leaning towards the valve head being the cause as the 57v is the reduced mains from the valve head where you've got 240v going in on the grey wire (with HW & CH off) which goes through a couple of resistors via a micro switch (SW1 in the diagram which I'll post) and then comes out on the orange wire to the boiler Switched Live (black). I'll post a picture of a typical 3-port valve head diagram, but I reckon that either the micro switch off the grey wire is stuck closed in this state or the valve body is sticking and preventing the motor from running freely and keeping the microswitch closed as I can't see what would cause this in the wiring centre, especially as the room stat is integrated into the programmer and we know the programmer is outputting ok in all 4 states.

 

[muffking]

 

[vikdab]

Viessmann advising me to connect a capacitor between orange and mains (they 1 and 96 - I think numbers relate to their board)

Will let you how I get on