Talk to me about CH timers/stats!

[NiceCupOfTea]

Hi all, we have a fairly standard central heating/hot water system. Recent boiler, but ancient CH timer and thermostat.

The stat is one of those 1970s/80s Honeywell electromechanical ones and I want to replace it with a digital one with a timer on it - that way I can leave the CH on all the time at the timer, and use the thermostat to trigger it/time it.

Looking at a Honeywell CM907.

Any obvious gotchas with swapping them over?

Also want to replace the timer. I have read a lot about a standard backplate and timers just attach to them - however, ours is an ancient Randall 4033 - I see they are still sold under the Danfoss name, but ours looks much older. When my parents got a new boiler in the early 80s they got one that looked identical to ours. It works fine but want more control over the timing for the hot water (rather than the 2 per 24 hours we have at the moment).

Is there a 7 day digital timer that will just attach to the same backplate?

[NiceCupOfTea]

Thanks guys - I'm OK with wiring up to a point but if it's too complicated I'll get my dad to have a look or call somebody in.

I understood with the stat that it's just a couple of wires so "should" be easy enough. If the Randall timer I've got is too prehistoric to have the standard backplate, surely it's just a case of swapping the wires over (assuming of course that it has all the same wires...)

[NiceCupOfTea]

Ferg -

Sorry, I don't know

I was hoping once I got the cover off the Randall box it would be relatively obvious which wire would go where in the new timer! I realise this may be a pipedream though If not immediately obvious I would "get a man in".

With regards the 'stat I am hoping it should be pretty simple - 2 wires iirc.

Would I be better off with the wired/wireless one? I was going to go wired as I thought that I would just end up leaving it in the wrong room or losing it. We don't have thermostatically controlled radiators - would wireless be better in this case?

[NiceCupOfTea]

Thanks for that - are there any CH timers that have an extra channel that can control an immersion heater? Always forgetting to turn the damn thing off...

[NiceCupOfTea]

Ferg said:

NiceCupOfTea said:

Thanks for that - are there any CH timers that have an extra channel that can control an immersion heater? Always forgetting to turn the damn thing off...

Not that I know of.
A heating programmer is fused at 3amps. Immersion heaters require 13amps.

Thanks - what I need is one that turns itself off!

[NiceCupOfTea]

Excellent!

So, a Honeywell CM907/927 to deal with heating/thermostat duties
One of these to deal with the Immersion heater.

But I still need something to switch the hot water. Any ideas? Something simple and one/two channel is fine (the heating "channel" would just stay switched on and be controlled by the CM927 but a 2 channel might be easier to wire in as it would just replace the 2 channel mechanical timer) but with a digital timer and an advance/override function.

Any recommendations?

[NiceCupOfTea]

andy43 said:

Something like this would do for the hot water.

So could I just replace the timer in the airing cupboard with that? Presumably I'd leave the old timer there as Ferg says it is a junction box. So how do I wire in a new 1 channel timer? In some way I need to bypass the other channel and allow to to be controlled by the stat...

[NiceCupOfTea]

Had a look at the system yesterday. In the airing cupboard there is the CH pump and two zoning valves. There's what looks like a junction box and some wires coming out to the CH/HW timer (by the way, the 2 systems work independently of each other), so I am hoping it should be "relatively" simple to change the timer as hopefully most connections are made in the junction box. However, if it's not immediately obvious I'll leave it be.

Don't want any bells and whistles, the old Randall timer would be fine if I could take 2 of the pins out - I just don't want the hot water on in the evening, only use it for showers in the morning!

The old Honeywell electromechanical thermostat has 5 connections numbered 1,4,3,2,5 from the bottom upwards. 1, 3, & 2 are connected. Don't know any more without taking it off the wall. Does that give any clues as to how wasy it should be to hook up the new thermostat?

[NiceCupOfTea]

Ferg, in theory how easy is it to identify the wires given they are just numbered? Multimeter whilst live or an easier way?

[NiceCupOfTea]

Very kind offer Ferg - haven't ordered the stat yet but will do in the next few days and give you a shout when it turns up if that's OK?

[NiceCupOfTea]

OK, got the stat (CM927) and the immersion timer, going to do them in the next couple of days.

It looks from the installation diagram with the CM927 that it needs all 3 wires - L (from timer), N, and the call for heat wire that goes to the boiler or zone valve, not sure which. The wires in the current stat (1,2,3,4,5 - 1,2,3 are connected) seem to correspond with here: - this would imply that:

1 - Live (from timer)
2 - Neutral
3 - Call for heat

I'll see how it looks when I get it off the wall...

In the meantime I've been looking at replacement timers. I think a 2 channel one may be easier to fit as there is already a 2 channel one there - even though the "heating" channel will be permanently on and controlled by the thermostat.

What I *do* want is:
- digital timer
- variable (1-3) on/off settings per day
- boost & advance settings

The Honeywell ones look good as always, but expensive. Somebody linked to a cheaper single channel ebay one (ST6100C) but with a long delivery lead time - really want to get it done in the next couple of days though.

Have happened across a Sunvic which seems to do what I want (207 XLS) http://www.heatingcontrolsonline.co.uk/sunvic-sele...
Any experience? Or would it be better spending more (double!) money on the Honeywell ST9400C http://www.heatingcontrolsonline.co.uk/honeywell-s...

[NiceCupOfTea]

Ferg, just had a look at the ACL Lifestyle stuff - I see an "advance" setting but not a "boost" - want to be able to push a button and have an hour of hot water and then switch off, rather than it stay on until the next "off" event in the timer IYSWIM!

Sunvic seems to be the best featured at a mini price. Some cheaper Honeywells on ebay but slow delivery...

[NiceCupOfTea]

OK,

I have thermostat waiting to go on.

Old thermostat has the following terminals connected

1 - red wire
2 - black wire
3 - blue wire

According to the doc on this page:

http://www.diyfaq.org.uk/docs/Sundial-Wiring-Rev1d...

(which is a more modern Honeywell electromechanical stat but seems similar to my ancient Honeywell stat, those terminals are:

1 - switched live from the timer/programmer
2 - neutral
3 - call for heat to boiler/zone valve

The new Honeywell CM927 has the following: N, L, L, A, B, C

According to the manual, for a zone valve setup N & L should be connected as expected to the switched lived and neutral, then you should bridge L to A, and the B wire is the call for heat wire to boiler/zone valve.

See here:

http://europe.hbc.honeywell.com/products/pdf/en0h8...

So - is this right? Should I bridge L to A?

[NiceCupOfTea]

Thanks for all the help guys.

CM927 wired up to the stat - L, N, B is call for heat, and L to A bridged

Replaced the Randall 4033 with a ST9400, L, N, HW on, CH on. That seems to be OK too!

Only slight annoyance is the "holiday mode" on the ST9400 holidays both the heating and hot water - would like it to holiday only the hot water and leave the heating to be controlled by the CM927.

I suppose I could just wire the CH on wire in the junction box to L and bypass the CH side of the programmer completely...

Replace the Immersion switch with that timer too, well chuffed.

The power of PH