Please help me change my SMC HW and CH timer

[Tim_Hodges]

Hi there,
My old SMC heating and hot water timer has begun to loose time so i have bought a new timer box, a MYSON 2MEP 2C.
The problem is that the wiring in the back of my SMC box has 8 inputs of the 10 possible and the MYson has only 6 possible inputs.

The wiring as far as i can make out on the SMC is the following, the inputs are numbered 1 to 10, 9 and 10 have nothing in them. I am not going to mention the earth wires.

1- red
2- black (1&2 from the same main wire)
3-blue
4-red + Black (both of these from the same wire)
5-black
6- yellow
7- red (3, 6 & 7 all from the same wire)
8- red ()5 & 8 from the same wire)

I am terribly confused and if anyone could possibly offer any help then it would be much appreciated. The furthest i have got is the 1 and 2 are probably the mains.
Thanks

 

[Chri5]

You need to work things back.

Within the main junction box for the controller there are various circuits.

* Power 240v live, neutral and earth
* Circuit for 3 way valve
* Circuit for hall thermostat
* Cirucit for hw thermostat
* Circuit for CH pump
* Control wiring for boiler

If you look on the new controller diagram this should clearly indicate what needs to be where, you problem is more to do with the lack of detail on the old unit. Try looking inside the junction box lid, sometimes the diagram is stuck on the inside.

Failing that, who are SMC- have they a web site to track a wiring diagram down for the current controller unit?

If you can't work out what's what then it will need a visit from a professional. I'm okay with central heating wiring and so are quite a few sparks, there are some who hate / loath control wiring. Best to seek the advice of a heating engineer unless your spark is confident with CH controls.

 

[Tim_Hodges]

The new box is very clear. The old box is a nightmare and the underside of the cover has no information on it whatsoever. My other thought was is the myson box actually compatible? I have no idea who SMC are and they don't seem to have a website. The only clue i have to what the box is is the SMC written on the front. Other than that there are no model details or anything. I'm really keen to get this sorted myself because i'm quite short of money at the moment, just a little confused.

 

[Chri5]

The new unit will work, it's just that you need to understand the old wiring first.

A controller is really just a series on off and on switches, CH on/ off, HW on/ off.

Do you have a traditional CH system? Does y-plan mean anything?

 

[Tim_Hodges]

I have been reading up a fair bit on the subject and saw Y system mentioned but to be honest i'm not totally sure what my system is. I have a floor standing boiler in the kitchen there is a thermostat in the Hall except except i have never touched it and then there is the hot water tank upstairs in the loft.

 

[Chri5]

I'd suggest you phone a local tradesperson and ask them to do the job.

I checked the Myson product and the on-line wiring detail is straight forward, but without the existing wiring being ID'd your on to a difficult process, one I fear is best left to someone who has a knowledge greater than ours.

 

[Tim_Hodges]

hmm bugger thanks for your help.

 

[Tim_Hodges]

Would i be right in thinking that the wire with a red, yellow, and blue is the wire from the hot water thermostat? i am slightly unsure as to why there would be a wire with a red and a black going into the same input

 

[smcandyt]

Hi Tim, Only seen your post today as I searched for info on the SMC CENTRAL HEATING BOILER CONTROL CLOCK UNIT (for the internet search)

Only a year late! same problem as above..

Although the whole system was installed by the previous owner in 1985.. it is still going strong today..

SMC control with Potterton Netaheat10/16.. the fan seized after mice had died nesting in it over the summer and new exchange unit was only £65 fitted!

Sometimes after being off all summer you have to hit the smc pump/valve with a shoe to get it going after a "plumber" quoted £650 to flush the system!!! and I decided to get it going myself...but appart from that everything is working well..

I had looked at this site searching for a replacement control unit for the SMC "clock" but ONLY because it's getting a bit loud and is next to the spare/guest bedroom..

I then rummaged through the paperwork we got with the house and found the instructions....

Hope this helps (Got the full set for the Potterton Netaheat 6/10 & 10/16 as well if needed...)

Here is the unit:

The wireing connector block:

The parts card info:

The diagram pic:

A zoom view of the relevant bit:

I hope that helps anyone who is replacing the unit, I'm a strong beliver in this is why the internet and forums like this are such a brilliant idea..