Room Thermostat wiring help needed...

Lars_UK1 · Monday at 9:55 AM

Hi all,

I am trying to replace my antiquated TLX SUNVIC (circa 1978) room thermostat with a Honeywell MT1 (THR830T)

I am a bit puzzled by the wiring though, as I thought it would be a straight like for like... can anyone help please?
See pictured below existing wiring vs wiring in mew thermostat.
When measuring with meter, it seems Blue has no voltage whereas Yellow and Red are live.

Also, according to the SUNVIC diagram, the yellow (open) cable goes to 1 on old thermostat, whereas in my case it was connected to 2 (close), and the blue goes to Neutral whereas in my case it was connected to 1 (open)...
Does this imply that in my case blue is open, yellow close and there is no neutral?
Is there way I can verify this using meter so nothing goes Kaboom?

Original wiring:

and Sunvic diagram:

New wiring (doesn't work):

wiring diagram for new Thermostat:

Help greatly appreciated.

Thanks

ericmark · Monday at 10:44 AM

The old mechanical thermostat does not need a neutral, by using the neutral the droop can be reduced, but it is not needed. It would seem the old thermostat is designed not to use a neutral, the new old is designed to use the neutral to reduce the droop (difference between on and off temperature).

So
3 Sunvic to 1 Honeywell
1 Sunvic to 4 Honeywell
2 Sunvic to 3 Honeywell

I have never seen a motorised valve which is powered in both directions, I am sure they did exist, but today the motorised valve is powered all the time it is open, and it is designed to work 24/7 stalled, and it has a micro switch that turns on the boiler, so boiler does not fire until valve is open. I found this advert which does explain the valve

Years of experience in the mastery of valve design and manufacture gives uniqueness to the products within our range.

more here not a clue why it does it that way, until I looked it up, did not even know it existed. I note a resistor shown between 2 and 3, not sure how not having it will change how it works.

jj4091 · Monday at 10:53 AM

Edit
Sorry eyes were deceiving me

EFLImpudence · Monday at 11:38 AM

ericmark said:
So
3 Sunvic to 1 Honeywell
1 Sunvic to 4 Honeywell
2 Sunvic to 3 Honeywell

NO

Live - Red - 3 Sunvic to 1 Honeywell
NC - Blue - 1 Sunvic to 3 Honeywell - if needed.
NO - Yellow - 2 Sunvic to 4 Honeywell

EFLImpudence · Monday at 11:45 AM

If the NC is not needed then the wiring could be rearranged at the other end of the cable to include Neutral.

CountryFan · Monday at 12:32 PM

Am I wrong, but may be the other red is Neutral with a possible blue sleeving? Hard to tell exactly from the photo. Also a black mark higher up or an I reading into too much?

EFLImpudence · Monday at 12:41 PM

CountryFan said:
Am I wrong, but may be the other red is Neutral with a possible blue sleeving? Hard to tell exactly from the photo. Also a black mark higher up or an I reading into too much?

That doesn't make sense.
I don't see any blue sleeving.
I think that red is part of the thermostat.

It is this diagram:

but terminal 3 is Live - Red - in all the diagrams

EFLImpudence · Monday at 12:46 PM

Now I have posted that diagram, I think Eric was right.

I will amend my previous post.

CountryFan · Monday at 12:49 PM

EFLImpudence said:
I don't see any blue sleeving.
I think that red is part of the thermostat.

Attached photo.

EFLImpudence said:
It is this diagram:
View attachment 400862

but terminal 3 is Live - Red - in all the diagrams

I can't see any coloured diagrams, only black and white. Ok, no worries, must have looked at the wrong diagram, apologies. I see terminal 4 on the Sunvic going to N?

EFLImpudence · Monday at 12:49 PM

Amended:

EFLImpudence said:
Shouldn't 4 & 3 on the Honeywell be the other way round?

NO

Live - Red - 3 Sunvic to 1 Honeywell
NC - Blue - 1 Sunvic to 3 Honeywell - if needed.
NO - Yellow - 2 Sunvic to 4 Honeywell

ericmark · Monday at 12:53 PM

EFLImpudence said:
If the NC is not needed then the wiring could be rearranged at the other end of the cable to include Neutral.

I do wonder if the SUNVIC motorised valve actually fitted?

CountryFan said:
Am I wrong, but may be the other red is Neutral with a possible blue sleeving? Hard to tell exactly from the photo. Also a black mark higher up or an I reading into too much?

I was at first thinking the same, until I realised this is a unique valve type,

These diagrams show how these valves work, it is motored off and well as on. I have never seen one of these

in the flesh so to speak, seems a good idea, but twice the price of normal valve.

EFLImpudence · Monday at 12:57 PM

CountryFan said:
Attached photo.

I still think that is part of the thermostat internal wiring.

CountryFan said:
I can't see any coloured diagrams, only black and white. Ok, no worries, must have looked at the wrong diagram, apologies.

There aren't any coloured diagrams. I only added "Red" because that is the colour used by the OP to terminal 3.

Still can't see any blue sleeving.

EFLImpudence · Monday at 1:00 PM

CountryFan · Monday at 1:06 PM

EFLImpudence said:
I still think that is part of the thermostat internal wiring

Yeah, it could be

EFLImpudence said:
Still can't see any blue sleeving.

A little bit of blue showing behind a little piece of metal if you zoom in. As I said, must have been reading too much into it

Harry Bloomfield · Monday at 1:20 PM

ericmark said:
I have never seen a motorised valve which is powered in both directions, I am sure they did exist, but today the motorised valve is powered all the time it is open, and it is designed to work 24/7 stalled, and it has a micro switch that turns on the boiler, so boiler does not fire until valve is open. I found this advert which does explain the valve

MOMO, Motor on, motor off. I got fed up with replacing my failed 3-ports spring return actuator, almost an annual task. I heard about MOMO valves and actuators, and so decided to swap, and give one a go. So far, much more reliable, no failure at all, though (as I have always done) - I do keep a spare head to hand, just in case.

Difference is - old spring return actuator, is under constant stress from the spring, when open, the motor has to be powered, but stalled, generating heat.

MOMO actuator has no springs, much less strain on it, and the motor is only powered when the valve position needs to be changed. Difference is, just a few electronic components. Unlike the spring return, the MOMO is only able to rotate in one direction, and the water valve, has to match the actuator.

I was so wound up with the unreliability of spring return actuators. I was looking to design my own version of a MOMO.

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Room Thermostat wiring help needed...

Lars_UK1

ericmark

jj4091

EFLImpudence

EFLImpudence

CountryFan

Attachments

EFLImpudence

EFLImpudence

CountryFan

Attachments

EFLImpudence

ericmark

EFLImpudence

EFLImpudence

CountryFan

Harry Bloomfield

DIYnot Local

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