Help Required ... 3 Way Valve not always switching to Hot Water

[Ray1000]

So fault unlikely to be valve.

You were right Eric

Recap ...

System Boiler, Three way valve, Nest Controls
Schedule ... 6am to 7am HW alone ... 7am to 8am CH alone
Problem was ... The last few days the HW hasn't kicked in at 6am but would if boost option was used.

Same again this morning, no HW response ... boosted for 30 mins at 0645.
The CH came on at 0700, noticed the rads got up to normal temperature.
(Always imagined the HW would take away from the CH)
Boosted again at 0715 ( The HW has been normal temp all day)

Set a new HW schedule for 4pm and stood at the side of the boiler ... nothing happened ... not a sound.

Assumed the problem was with the Nest or the connection between my phone App and the thermostat.
Checked the schedule on the wall mounted Nest Thermostat and found the extra 4pm one was showing ruling out the App
During the course of checking all the settings on the thermostat dial I found the problem ... " Water Schedule Disabled !!! "

Sorry to have troubled you and thank you all again for your help



Ray

 

[Ray1000]

PLEASE SEE PREVIOUS POST RE ORIGINAL QUESTION

That pump orientation is frowned on by Grundfos

Not sure if my earlier picture gave the wrong impression of the pump orientation ? It's in a vertical pipe.

 

[Johntheo5]

Before the last few days hiccup, have you ever programmed both the CH and the HW on together, I wonder how does the nest deal with this, if requested.

 

[Ray1000]

Yes it’s no problem, I always had them separate until this morning. Now I know they are well balanced I might start the HW at the same time as CH 7am

 

[DP]

Thank you, sorry for any confusion … my only issue is … the hot water isn’t coming on in a morning as set by the Nest schedule
6 - 7am HW only
7 - 8am CH only if below temp

When hot water not coming on, best thing to do is get the multimeter out and locate the reason why it is not coming on.

For hot water demand, HW call terminal will go live
This will then be extended to C terminal of the cylinder stat
Calling terminal of same stat will be live making orange wire live which fires the boiler

If boiler fails to come on, perhaps the water is still at temperature and does not need to be heated.

If immersion heater has been left on, boiler may not fire

Best to fault find rather then speculate

 

[DP]

Yes it’s no problem, I always had them separate until this morning. Now I know they are well balanced I might start the HW at the same time as CH 7am

Starting hot water earlier means water hot when you need it

The valve does not move from no power position or home position for hot water call
Boiler run is through cylinder thermostat

For ch call, the white wire goes live and valve motors to mid position where it is locked in with rectified voltage

Assume now hot water is satisfied or hot water timer goes off. Grey wire gets power. Valve motors to end and boiler energised from orange wire

 

[Johntheo5]

A frequent theory/fact? for the relatively short life of MPVs is their last port of call which is nearly allways CH, so even when the CH is programmed off for the night then the valve is still powered on overnight, I know someone who modified the wiring years ago and the MPV is still working nearly a dozen years later, I recently came across a neat schematic of how I imagined he did this, attached.

 

[Ray1000]

Best to fault find rather then speculate

I understand.
This was my way of fault finding, in the absence of a multimeter and your in-depth knowledge of the valve wiring.
I first thought it was the contact intermittingly not making it inside the valve head.
It was certainly caused by the HW schedule being disabled somehow.
I'd never seen that setting before, but now I have it'll be the first thing I check if it happens again.
Thanks
Ray

 

[Ray1000]

Starting hot water earlier means water hot when you need it

In our case with the 6am to 7am HW and 7am to 8am CH it also means the boiler water is is up to temperature when the CH starts.
Having now tried them starting at the same time I might stick to it.
I had my views coloured by having an Ideal Classic boiler, presumably holding more water than our new loft located Logic, in a detached garage with all the extra pipework it entailed ... I got £150 for the scrap copper !

 

[Ray1000]

.... their last port of call which is nearly always CH, so even when the CH is programmed off for the night then the valve is still powered on overnight,

I need a way to resolve this if only to reduce the chances of our occasional valve buzzing happening in the night.

I'll start by manually flicking the HW on for a few minutes last thing.

One problem with the Nest is it only applies 30 minute intervals

Thanks
Ray

 

[DP]

I need a way to resolve this if only to reduce the chances of our occasional valve buzzing happening in the night.

I'll start by manually flicking the HW on for a few minutes last thing.

One problem with the Nest is it only applies 30 minute intervals

Thanks
Ray

As a heating engineer 30 years under the belt, I see Nest etc a designer item compared to programmers from makers that have been on the game longer than my years battling all sorts of issues.

My go to programmer is Honeywell Lyric that has more feature than a Nest world have

I take it you have got a system bypass in place

 

[Johntheo5]

Manually switching on the HW for a few minutes is fine as long as the cylinder stat is calling, won't work otherwise, the relay in the above schematic ensures that the actuator is powered either fully or partially only while there is a demand for CH, it will all ways return to the unpowered state.

 

[Ray1000]

I take it you have got a system bypass in place

I think so - in a fashion - pressing the button at the side of the Nest Stat shown in an earlier picture puts both CH and HW on.
While the tank stat would control the HW I'm not sure about the room temperature under these circumstances.
I'm not sure where the actual thermostat is, but if the Nest ring were thought to have failed it would be a matter of trying another one ... it simply clicks into place.

What would be a good stand by for the Nest system failing ?

 

[Ray1000]

Just out of interest we’ve now got the HW & CH coming on together at 7am to 8am and it’s working fine.

Thank you again for your help
Ray

 

[Mister Banks]

Just out of interest we’ve now got the HW & CH coming on together at 7am to 8am and it’s working fine.

Thank you again for your help
Ray

There is an argument for having the HW schedule separate from the CH schedule to improve boiler efficiency.