Honeywell V4073A testing.

[ninjasta]

Tecently noticed that the hot water is only working if there heating snd hot water demand.
Valve is position A for heating and is ooening hot water position B.
With both heating and hot water flow goes into both sides.
The system is y plan. I fsrly new to the house and had new boiler with google nest controller installed.
They left the honeywell and cyclinder thermostat in place.
Often some testing I have.
The V4073A1039 model 3 way valve seem to parked in position A.
It nest controller commands hot and cold flow goes in both A & B. With hearing satisfied boiler goes on/ with heating demand.
The hotwater timer doesn't move the valve to hot water only.
The motor housing on the valve is warm even there the pump is off.
Hot water from nest programme turns pump but not the boiler. Which eventually stops despite being commanded on by the timer.
If I push room thermostat up to high enough create demand on the flow goes into both sides untill and boiler fires to provide heat.
The cylinder loks fairly old and simple L641A1005 unit. It does click If push the bimetalic strip.
questions
1 Does 3 way remember the last actuated position?
2 as mid shouldn't always from the mid position?
3. Finally is return spring internal the actuator or valve body?

I suspect that the cylinder thermostat is at fault in that it's sending demand signal.
If unit is a compatible replacement?
Thanks

 

[CBW]

It could be a wiring issue with the Nest. Yes spring return is part of the actuator. It’s not the easiest to follow your post, it could also be an actuator fault.

 

[ninjasta]

The nest and boiler were professionally installed. So I would the followed y plan when wiring when installing it.
To heating only - boiler fires.
Heating plus hot water demand. Get both hw and ch.
Hw demand only - pump starts then stops when doesn't start. But valve doesn't appear to move. Tho my old house used dyrson there's no position indicator. Lever is free to move without resistance.

 

[ninjasta]

The wife chip failed so nest controller needed replacing. Have with and without hot water for hest and see same behavior.
If acwiring diag fir (obsolete) L641A1005?

 

[Johntheo5]

If you switch off the CH at the programmer and switch on the HW only and ensure the cylinder stat is calling. ie, turned up to say 65C, does the boiler fire up?, there should be resistance at the lever.

 

[ninjasta]

No with HW and Thermo on max pump starts with preheat boiler function. After preheat tomer expuies pump stops boiler doesn't fire.
Nest in manual puts both hw an ch and both a and b outlets get hot. Then only hot. Then boiler stops run till run timer expires. Pump runihg hw gets hotter, outlet A gets slightly cooler compared to hot water out during pump run on period.

 

[Johntheo5]

I have seen it mentioned in some posts that the HW will only heat if boost is selected unless the Nest is told what type of boiler is installed, write
"Nest Y plan" in the search box, above right, there is all sorts of info available from the posts there.

Also have a look at these basic Y Plan schematics to give a idea of how the "641" cylinder stat is wired

 

[ChrisJP]

The wife chip failed

What's a wife chip? I'm sure my wife doesn't have one!

 

[ninjasta]

With nest controller you can to set both hot water and heating the default only commands hot twice per for about 1 hour. Which whilstv enough maintain yemp won't heavy use e.g shower bath.

The nest thermostat pairs via wifi mesh to its heat unit slave. Which has a simple soc driven set of solid state relays which provide switching for heating and hw. The relays functionally identical any clock based controller.
It was professionally installed along a new boiler (Vailant ecoflex pro).
I traced the wiring it connected as per the y plan std. Fault is either the 3 way actuator or thermostat.
Whilst the boiler and nest unit still in warranty, as they didn't change either the actuator or cylinder thermostat they aren't covered.

 

[Johntheo5]

To check that the valve is spring returned to its HW (B) position, switch off the electrical supply, there should be resistance immediately you start pulling on the manual lever.

Suggest next, programme CH & HW programmed On, ensure CH thermostat and cylinder thermostat turned down (not calling), restore power, again check for (immediate) lever resistance.

Turn up cylinder thermostat, check for (immediate) lever resistance, (boiler should also fire up).

Turn down cylinder thermostat, turn up the room thermostat, check for "floppy" lever (no resistance), valve should then have moved fully over, boiler should fire and (CH) port A pipe only should get hot.

Turn up the cylinder thermostat, valve should move to mid position and both CH port A pipe and HW port B pipe should be hot. If this happens then there is NOT a cylinder thermostat fault.