Replacing room thermostat Drayton RTC

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Have a 25+ year old CH system, but the room thermostat now seems to be 'going'. The current one is a Drayton RTC (shown below). I the hope I could work it out I bought a Drayton RTS8. I thought it might be a bit tricky but I am now a bit lost as to what wires go where from old to new, and not sure even if the new RTS8 will work with what I have. Any assistance appreciated. I have picture of all the parts but not yet work out how to post them!
Have very basic CH knowledge but know electrics quite well.
Ben
 
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20160624_172426.jpg
 
An Earth, 2 red, a black, a blue and a yellow.
 
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Well that's a lot.

Looks like you have a 3+E (red, yellow, blue) and a 2+E (red, black) though one of the earths has probably been cut off, and the previous installer couldn't afford 0.5p for some G&Y sleeving.

I was expecting just a 2+E, which is usually all you need on an old system. 3+E enables you to run an accelerator heater inside the stat case. Either makes the swap easy, but you seem to have both.

I wonder what the others are for.

Has it had a new timer fitted, since the boiler went in? Or some other change?

Is there a circuit diagram on the lid?
 
Nope all original no changes at all. But yes circuit diag on the lid of thermostat.
20160624_172434.jpg

Sorry photo not great.
 
What does the LH red connect to? It's not normally required for heating; it's used in cooling systems.

Also, there are two wires connected to the N terminal - blue and black. One (blue?) should be in the same cable as the yellow and RH red. What does the other one connect to? Is it in the same cable as LH red?
 
Not sure so I will have to look at the the other ends and see if I can find out. Will take a while as can't do it this moment - maybe tomorrow. Thanks so far.
 
It looks like you could have a MOMO valve, motor on motor off which requires both power for on and off. I can't find documentation for RTS8 as its not listed on the Drayton website. The stat will need at least Common, NO and NC terminals.
 
It looks like you could have a MOMO valve, motor on motor off which requires both power for on and off.
Were MOMO valves around 25 years ago? Sunvic had a patent on them in 2004, but it's expired as they wouldn't (couldn't) pay the renewal fee.

The Sunvic MoMo valve used exactly the same wiring as spring return valves.
 
No idea. The ones I've seen, don't know what brand, had separate open and close wires.
 
I can't find documentation for RTS8 as its not listed on the Drayton website.
FYI, it's also known as the CombiStat.

If the OP's system requires a connection to the Sat terminal of the thermostat, then the CombiStat/RTS8 is not suitable as it doesn't have a Sat terminal. The RTS4, RTS9 or RTS10 would be required.

 

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