Simple job....got me stumped !

[mondriver]

Hi guys.

I'm a newby here. Great forum.

I've just spent the last 45mins trawling through my search results to loads of permutations to a problem, and can't seem to find what I need, so apologies for starting a new thread.

I have an old Honeywell mechanical thermostat for my home central heating.
I want to replace it with a new Honeywell DT200 digital thermostat.

The problem is, my old themostat has four wires. Two are red (live?) wires going to individual inputs to the thermostat, and another two black wires going to a common input on the thermostat. The new DT200 wiring diagrams look completely different to the old unit.

I am stumpped.....

Anybody go an idea on how I should proceed?

When I put a voltmeter to one of the reds and the common blacks, I read 240v and 0v as the pump kicks in and out. Using the other red, I read 0v when the pump is on and 240v when the pump is off!, and 240v constantly from both reds whether the thermostat is on or off.

Any help would be really appreciated!!

Thanks in advance.

 

[PEDANTICVINDICTIVEMAN]

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[mondriver]

PEDANTICVINDICTIVEMAN

Thanks for the constructive help.


What may be obvious to you, may not be to others. I thought that's the point of a forum like this.

...i must have been wrong in your case.

 

[PEDANTICVINDICTIVEMAN]

Yep

 

[mondriver]

Very good....now that you're getting your post count up.

Some inspired comments to about 8 threads.

You're a credit to the forum.

 

[PEDANTICVINDICTIVEMAN]

yep

 

[wilhelm]

phone honeywell. cos, errrr i would.this isnt that clear. i can make out a few components in diag 5.
but its p£ss poor wot the f£ kk is a m452/vm19?? or is there a page missing?

 

[Soggy_weetabix]

Colours mean nothing! (Red=live...why?)

If I understand Part P, then this is expempt as its a direct replacement.

Remove old stat and work out "what does what". Not technical but if your wanting to change that stat, this is basic stuff.

Find your common, call for heat, neutral and earth (if if has one).

Maybe you have a closing sequence if you dont have a honeywell motorised valve?

David

 

[mondriver]

Thanks soggy_weetabix
Yeah...that was basically my conclusion. I think it's more of a "work it out for yourself" rather than go by their diagrams.

....unless of course you are PEDANTICVINDICTIVEMAN, then you could do it in your sleep.

 

[MANDATE]

I can't think why you would need four wires. Two lives going to seperate terminals and two blacks (switched live I presume) from the same terminal.
I think you have to get a better understanding of your existing system and find answers to the following.
Two blacks from the same terminal suggests it's feeding two loads. One I presume is the pump. what could the other be? boiler? You could remove one to find out.
Next what makes each of the reds 'live'? The Programmer/Timer will make one live when CH is selected but does the programmer make the other one live also under the same conditions? if so why?. if not what's the difference?
The fact there are two lives suggests they are coming from different sources and if you could trace these it may help. Also the two terminals which the lives go to may well be linked together internally, in fact I think they must be. You can easily confirm this.
When you have confirmed this the wiring of your new stat should follow the same method ( 2 red live 'in' 2 black switched live 'out')
Hope this make sense

 

[Nige F]

Yep

livin` up to your name Yep yep

 

[MANDATE]

Hi mondriver! Did you manage to solve your problem. It would be interesting to know if the two live reds were linked and where they came from.

 

[mondriver]

Hi

Yes...problem was solved.

I was looking too deep into it. In the end it was just a simple circuit cut "in series". I discarded the neutrals and used the two lives as a series connection.....that was it.

Thought it was far more weird than that really....


Thanks for all the CONSTRUCTIVE posts....

 

[Paul Barker]

Thanks for cheering me up pvman.

 

[corgiman]

PV man FOR PRIME MINSTER


YEP YEP