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    How can I replace my mechanical Central Heating timer with an electronic one?

    I've noticed a few electrical questions getting answered quite comprehensively. Here's one that's been bugging me for a while and I suspect the answer is simple. If it is, I'm on it, but can anyone who knows please advise...

    Can I simply swap my mechanical central heating timing with an electronic one? It's fairly new, driving an on-demand hot water and central heating gas combi-boiler. I'd like one I can program for different times for each day, noting the differences between weekdays and weekends, etc.

    At the moment I have the sort with a circular 24hr timer section with 4 coloured tags you move to set the on/off times. It's very inaccurate. It has a switch for On, On all Day, On Twice, Off, and it has an advance button.

    If anyone can suggest a good replacement, that would also be great.

    Thanks in advance.

    15 Comments

    Yes it's fairly straight forward for a competent person.

    A mechanical timer "throws a switch" when it passes the relevant "plug/setting" and this sends the power to the unit

    A digital timer will just do exactly the same (just ensure you have the correct rated timer).
    Edited by: "philphil61" 17th Dec 2014

    I would say yes . The wires at the back on the old timer will be the same ones used for the new timer .I think you'll need a sparky to fit it though .
    Have a look :http://www.screwfix.com/c/heating-plumbing/central-heating-controls/cat831042

    lots of different ones , some with built in thermostats at different prices . Have a word with your electrician and ask what one he would recommend.

    Hi, I would bet yours is a Horstmann 425 Diadem or Tiara, is so the direct plug in replacement using the existing backplate is the ChannelPlus H27XL, available from lots of places

    I recently replaced the mechanical timer on my boiler with Drayton LP711 from Screwfix, not a straight swap as no existing back plate but easily done.

    Original Poster

    So, mine's a Siemens RWB30E, the instruction manual says it's fitted with "an industry standard back plate". I was hoping I could pop this off and pop a new one on. Is it not that simple? Reading some of the screwfix items, they say they fit x or y backplate. Mine doesn't say what sort of backplate, so I presume they can be wired differently?

    I would say contact Siemens directly and ask them which modern controller you can fit directly on the backplane, they're very good so I'm sure they'll get you sorted v quickly.

    Siemens Heating Controls
    Electrium Sales Limited
    Commercial Centre
    Lakeside Plaza
    Walkmill Lane
    Bridgtown
    Cannock
    Staffordshire
    WS11 0XE
    Tel: 01543 455000
    Fax: 01543 455033
    Helpline: 0870 850 0184

    philphil61

    Yes it's fairly straight forward for a competent person.A mechanical … Yes it's fairly straight forward for a competent person.A mechanical timer "throws a switch" when it passes the relevant "plug/setting" and this sends the power to the unitA digital timer will just do exactly the same (just ensure you have the correct rated timer).


    That 'was' useful 'information'.

    Original Poster

    Thanks all. I've followed your leads and done a little more reading, which I probably should have done in the first place. I think I can figure out how my back plate is wired, and I think I'll be able to work out if a new timer will 'drop in' using the same wiring. One I've looked at won't, as the leads are not in the same place... so here's the next question:

    Is it legal for me to move the wires over on the backplate? I know certain electrical work requires a proper sparky to do it, is this one of those cases?

    Tony68k

    Thanks all. I've followed your leads and done a little more reading, … Thanks all. I've followed your leads and done a little more reading, which I probably should have done in the first place. I think I can figure out how my back plate is wired, and I think I'll be able to work out if a new timer will 'drop in' using the same wiring. One I've looked at won't, as the leads are not in the same place... so here's the next question:Is it legal for me to move the wires over on the backplate? I know certain electrical work requires a proper sparky to do it, is this one of those cases?



    It is legal for you to do it. The law (17th Edition Wiring Regulation) are intended to manage and regulate new installations and those that carry them out. The bulk of it is how circuits are designed and installed and less about the devices that these circuits feed (ie your time switch). You won't be prosecuted just for doing the swap, though if you get it wrong and kill someone in the process then yes you could be prosecuted.

    Original Poster

    Sorted. Thank you.

    If you are with British Gas it's £150.00 to have a Hive fitted.
    You get a great timer plus can control your boiler with you phone over wifi.
    Or its £200.00 if not with them.Thay say can save you cash in the long run.

    Original Poster

    seanj007

    If you are with British Gas it's £150.00 to have a Hive fitted.You get a … If you are with British Gas it's £150.00 to have a Hive fitted.You get a great timer plus can control your boiler with you phone over wifi. Or its £200.00 if not with them.Thay say can save you cash in the long run.



    Thanks for the comment. That is very interesting. I did a little reading and I'm now struggling. I like the concept, but I also like the concept of having all my rad's controlled. At the moment we have a thermostat in the hallway and TRVs on most of the radiators. I'm not sure how good these single zone devices are, I barely know how to control the system I've got - like how does my hallway thermostat work when I have TRVs?

    I'd be interested in hearing if you think £150 on a smart hallway thermostat would actually give me any savings beyond what my TRVs give me? Saying that, £150 on a new smart programmer, professionally installed isn't that terrible, so I wouldn't need to make that much saving to get my money back.

    Standard backplate is the 6 pin type, there are lots of straight plug in replacments, there are apps available for this process which are very good, and throughtly researched.

    Competent person only required if retro fit. A new system need part 17 spark. A householder is competent person but only if competent.mcb will switch off before it kills!

    Original Poster

    I really appreciate all the comments on this. I'm going to give the Hive some serious reading, especially on what savings I could realistically make. Having variable temperature settings across the day sounds like I'll start saving money instantly. Added to the ease of being able to boost it on days I work from home, or turn it down when I'm not about.

    It just seems that as its only got a single thermostat, it won't be as efficient as it could be, but I guess for £150 I can't expect a complete house-wide system, I think I'm looking closer to £750 for that.
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