Nest 3G wiring help

[Arb]

Hi all, this is my first post so please be kind.

I installed a Nest thermostat a few months ago I have a gravity fed system powered by a Baxi Bermuda Back Bolier, I have a Honeywell 4043 2 port valve, I based the insatallation around a c plan as the wiring appeared to follow this logic although I never traced all wires to confirm this as the installation appeared to work without problem.

My issue is as the weather has been getting colder and I use my heating more I noticed the water was getting scalding hot, I have checked my 2 port valve for function and bar removal to check the micro switch it all appears fine, obviously the thermostat could also be the cause.

Although I am beginning to believe I have wired the Nest incorrectly, as I cannot call for hot water, so the water is heating whilst the radiators are running constantly and not shutting down.
Essentially when calling for heat I am also running the hot water.

Can someone have a look at the pics and tell me if I have done something wrong?

First pic is the junction box, the only change I made here was to bridge from 4-5, now I forget the terminology but this was my room thermostat which was removed as I now have a wireless Nest thermostat so now the heat link is what calls for heat.

Second pic is how the heat link is wired, this was an exact copy of the wiring from my old Honeywell ST799 programmer.

Any thoughts or pointers, I should add I cannot call for heat separately either, currently hot water is set to off.

So confused right now

 

[Leesparkykent]

do you have a cylinder thermostat?

 

[Arb]

Yes, I have it right down to 50 degrees.

 

[mydigitalhome]

Hi, why do you have a blue wire on the earth terminal of the next box?

 

[davesparks]

Hi, why do you have a blue wire on the earth terminal of the next box?

He doesn't, the blue is in the T1 terminal

 

[davesparks]

For a true gravity system you wouldn't normally have any valves, the hot water channel fires the boiler with the heat gravitating to the cylinder and the room stat would run a pump which just pumps around the radiators. Thus for heating to Ben on the hot water must also be on.

What does the valve in your system do? Is it on the cylinder coil? What operates it?

And I must congratulate you on that beautiful bit of non-compliant installation work, I wish I could install things in a potentially dangerous manner like that!

 

[Arb]

And I must congratulate you on that beautiful bit of non-compliant installation work, I wish I could install things in a potentially dangerous manner like that!

Ha Thanks Dave yeah I know..... Its a long story and I'd be more than happy to go over it with you but this thread is probably not the place.

Long term goal is to replace the whole system and get the Baxi back boiler out of the fireplace and a log burner installed.

The valve is on the cylinder, thermostat runs to programmer (now the heat link) which in turn is also connected to the two port valve which has 4 wires (5 if you include the earth, 2 shades of brown, white and orange)
Now I am guessing here the 4 wires are to open the valve and turn on the boiler independent of the CH.

 

[davesparks]

Ha Thanks Dave yeah I know..... Its a long story and I'd be more than happy to go over it with you but this thread is probably not the place.

Long term goal is to replace the whole system and get the Baxi back boiler out of the fireplace and a log burner installed.

The valve is on the cylinder, thermostat runs to programmer (now the heat link) which in turn is also connected to the two port valve which has 4 wires (5 if you include the earth, 2 shades of brown, white and orange)
Now I am guessing here the 4 wires are to open the valve and turn on the boiler independent of the CH.

Haha indeed, it's good that you can laugh it off and have a long term goal of replacing it, it's not like the regulations exist for a reason or that electricity kills within a fraction of a second is it!

So the cylinder stat should shut the valve when the cylinder has reached temperature. They are very unusual colours for a two port valve, it would normally be brown, blue, grey and orange (plus a white on a 28mm valve)
You'll need to bell out the cores that yours has to establish which is the motor and which is the microswitch.

I think the main problem you will come up against here is that the Nat is just not suitable to control a gravity system,

 

[Dave OCD]

And the designer of those heat links needs a kick up the @rse , silly little terminals that are a pain to get two small conductors in and could they have got the cable clamps any closer to the terminals ?!

 

[davesparks]

And the designer of those heat links needs a kick up the @rse , silly little terminals that are a pain to get two small conductors in and could they have got the cable clamps any closer to the terminals ?!

Yes, it's a pain, personally I use extra cores and only connect one conductor to each terminal

 

[Arb]

Thanks Dave, and your contempt is duly noted, please do not think of me as wreckless, although I am in no way a professional, forums are not good at conveying emotions my little laugh was more one of embarrassment than one of who does not give a...

The colours is what throwing me, and the fact nothing is labelled-it all looks very old, other than the earth wire I have used as a bridge (yes not compliant I know) that's the only change I have made even the T1 and T2 on the heat link are the original room thermostat wires reused.

I will check the 2 port valve with a meter tomorrow. Although I would of expected something to happen when calling for heat through the Nest wireless controller?
Would not disconnecting the stat on the cylinder cause the valve to shut or do you have another idea.

Again thanks for your patience and offering advice.

 

[Dave OCD]

Yes, it's a pain, personally I use extra cores and only connect one conductor to each terminal

Me too, 5 core flex is very handy.

 

[Arb]

Dave i had another look as I was doubting myself, and you are correct - brown, blue, grey, orange and white as it's a 28mm valve.

 

[Leesparkykent]

It should be a 28mm valve if used on a gravity setup so you have the white which is normally closed that can fire the boiler when only the heating is calling.

 

[Arb]

Okay got hold of a meter today and checked everything thoroughly, everything is wired correctly and doing what it should when required, I never realised the 2 port motor could take so long to react or be so quiet in operation.
When the programmer calls for hot water and the cylinder stat is not satisfied after 20 seconds the boiler fire ups and everything works as it should, when the stat is satisfied the valve motor operates and the boiler shuts off.

Which leads me to the only reasonable conclusion that the valve itself is faulty and not sealing.

 

[Dave OCD]

When the stat is satisfied the valve actually closes on a spring return as power is removed from the motor - unless it's a 3 port valve which is slightly different.

 

[Arb]

When the stat is satisfied the valve actually closes on a spring return as power is removed from the motor - unless it's a 3 port valve which is slightly different.

Yes which appears to be happening yet hot water still gets through. I have an older Honeywell valve and can only take it apart so far before bad things happen, I can remove the synchronous motor and that's about it.
I will buy a complete unit to fit in the new year as I am satisfied that I have exhausted all avenues and have a pretty firm diagnosis that the valve is not seating for one reason or another.

Thank you all for your professional help and not being to brutal about my amateur efforts and non compliance.

 

[diditrain]

When you are calling for heat only, have you checked for voltage on the brown conductor of the valve?

 

[Arb]

When you are calling for heat only, have you checked for voltage on the brown conductor of the valve?

No I didn't, although I did disconnect the stat to the valve for 24hours so 0 Volt to the motor and hot water was still getting past, the case states the valve is normally closed so I assume it's not seating correctly. Once the stat once connected it functioned as it should along with the motor operating and boiler firing.

But I will double check over the weekend just to be sure.

 

[freddo]

When the wires to the nest receiver come from behind, use the rear knockout holes, that's what they are bloody there for!!!!!!!!!!!

Whoops, missed the date!