Updating old dial stat to wireless digital

Discussion in 'Electricians' Talk' started by lausie, Nov 6, 2018 at 9:43 AM.

  1. lausie

    lausie New Member

    Hi all,

    My old dial room thermostat stopped working earlier this year. It was a Drayton RTS8. I had a boiler engineer out doing the annual service and as a quick (stupid) fix, he disconnected it at the boiler and suggested we run off the built-in on/off/timer if we need heat.

    Anyway, heading into winter now, I'm looking at sorting it out and would quite like to put a wireless jobbo in. I'm intending to put the receiver where the old dial was, so as to tap into that wiring and avoid having to repair the old site and/or run new wire. The stat can then sit in the living room which is always out of sync heating wise, as it's a disproportionately large room compared to the rest of the flat.

    The old stat is currently served by 3-core +e. Live (brown) to L, Switched Live (black with brown sleve) to 3, Neutral (blue) to N, and Earth (yellow & green) to the earth term. See pic:

    IMG_20181105_140757~01.jpg

    I know it would be ideal to run 4-core to the new RF, but can I make do by bridging L to Com? The boiler is fused down to 3A.

    Alsoooo, as the boiler guy removed the stat wiring from the PCB, I need to re-hook that up. There are two terminals in there, marked as TA 1 & 2. After removing the stat, he looped the two terms together, but as theres only one wire (black (with brown sleve), does it go in 1 or 2? The Live is attached to the Perm L.

    The boiler is an Arriston 27 MFFI. Wiring diags here: http://library.plumbase.co.uk/flipbooks/RE/arbmffi27aco_21179_t/mobile/index.html#p=27

    I'd probably be looking to go with a Hive or perhaps the Salus IT500. Mucho pounds, I know, but I've been stuck in the dark ages for so long, I'm trying to future proof!

    Thanks in advance!
     
  2. Muzungu

    Muzungu Active Member

    Just put in a Salus 510rf, not internet but RF which is fine for me. Same wiring as yours, linked L to Com. Receiver screws into back box and take the thermostat/controller wherever you want in the house (comes with a stand). Obviously can't connect to it while not in the house so can't make a display of switching on the heating from your phone just before leaving the pub :). £40 or thereabouts.
     
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  3. lausie

    lausie New Member

    Ok thanks - still deciding between wireless and smart wireless, but I gather receiver installation is pretty much the same, save for plugging a dongle doodah into the router.

    It's just the boiler end I'm scratching my head over now.

    Is it right that only one of the two 'TA' terminals will be used? In volt free setups, I gather you'd use both, but as this is 230 switching, do I simply hook the black up to one of the TA terms and then feed Live from the spur?

    Does it matter which of the two I use? Presume not, but don't want to fry my PCB!!

    It's looped off at the mo after the boiler guy disconnected the old dial stat, but there's only one wire term-free...

    IMG_20181105_202441~01.jpg
     
  4. Mike83

    Mike83 Active Member

    You’ve got options.
    You could fit a receiver next to the boiler and wire it in with 5 core.
    Or
    Fit a receiver were the current stat is but you need to ensure the boiler switches 230v to utilise the cable that’s present.

    Either these option will allow you to fit the new thermostat in the lounge. This could lead to issues with trv’s interfering with temp.

    Both ta terminals could be used but as only 1 has we can assume the boiler switches 230v.
    Disconnect the link and one of the terminals will have 230v. The other terminal with no voltage would then be the heatings switched live.
     
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  5. lausie

    lausie New Member

    Thank you Mike, that's a massive help!

    We have TRVs on both rads in the living room but they're always set to full. The prob is, the hallway is tiny, so heats up really quickly. The living room, however, is 7m by 6m, and just doesn't seem to get up to temp.

    I work from there, so would rather have a hotter hallway and bathroom, than a cold work area. The bedroom is set to low on a TRV so that shouldn't be a problem.

    Thank you again, much appreciated!
     
  6. Flame

    Flame Member

    I've just installed Hive to my combi boiler. i put the Reciever next to the boiler with 5 core. You could do the same and use the Hive thermostat to cover previous thermostats mess, It's a bit of a unit to be fair! that's preference though i guess, i know you can get pretty stands to go with them for a silly price :p
     
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  7. lausie

    lausie New Member

    I've given that some thought but the issue I have with the unit in the hall is that the temp is a bit out of sync.

    The hall is the smallest area in the flat and heats really fast. In comparison, the living room is much bigger and doesn't reach temp before the hall stat is shutting things off. I guess I could compensate by turning the stat higher, but figured having it in the living room would sort out the prob!

    Will give this some more thought tomorrow!
     
  8. MGW

    MGW Well-Known Member

    Looking at the linked manual seems the control is extra low voltage on terminals TA, as to type of thermostat there is a lot to that boiler with outside sensors so not sure what is required. There are three types of thermostat, as far as I can see there is no option for using one connected to eBUS so has to be on/off type, these are again split into two types, with or without anti hysteresis software. Every time a boiler switches off any heat in the boiler is lost out of the flue, so economy wise you don't want anti hysteresis software, the job of the thermostat is to switch off the boiler when it is warm outside, however that is theory. In theory the TRV controls room temperature.

    In practice however many use a wall thermostats to control the main room, and having anti hysteresis software does give better control even if it costs more to run.

    The problem is with wired you can select both types and both work well, but with wireless having no anti hysteresis software seems to go hand in hand with no fail safe. The Horstmann HRFS1 looks great, cheap and programmable but if the batteries go flat, or even if some thing else stops signal it will just continue doing what ever it was doing before, so can stick on heating. The Honeywell Y6630D looks rather expensive in comparison however if no signal in 1/2 hour it will auto close down, and it also has anti hysteresis software.

    So if you have the wires than a Flomasta 22199SX is better than both, as fails safe and no anti hysteresis software plus cheaper.

    What anti hysteresis software does is before it reaches target temperature it starts a mark/space ratio switching the boiler on/off and slowly increasing the off time so it does not over shoot. However if you fit better heads on the TRV starting at the Terrier i30 which is about the cheapest, that can also have a time set to vary temperature through the day, and instead of switching on/off it slowly reduces or increases water flow, which in turn makes the boiler flame alter to suit, the flame modulates rather than switching on/off which is far better.

    Likely best is EvoHome where the TRV heads talk to a central thermostat which in turn switches boiler on/off as required, with better boilers it can with the eBUS control flame height, but seems your boiler is not OpenTherm enabled, which is why for you the i30 is likely a better option.

    I am not saying electronic TRV heads work A1, because the TRV will continue to open to try and get room to temperature with cheap versions even when boiler is not running, when boiler does start up unless the lock shield valve is set right it can over shoot, so times on valves need to follow times on programmer.

    But once set then if set to 20 deg C that's what you get, there is compensation for water temperature so even though right next to radiator they still keep room at set temperature.
     
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  9. Allsorts

    Allsorts Well-Known Member

    I think what you propose is fine and should work.

    For the hall, turn the lockshield valve down an eighth-turn at a time, allowing a few hours to check the effect - you essentially want it outputting at a lower rate. Ditto with the bathroom if you want.

    (Probably actually worth first closing the hall and bathroom lockshields off fully - clockwise - and counting the number of turns and part-turns that takes, and then you can reopen it and go from there. The reason is, there's a chance that it was never actually set properly so could be open numerous turns, in which case trying to close it down an eighth-turn at a time would take weeks...)

    No reason to not fit the receiver where the old stat is - makes sense to use that location and wires rather than patch it up. You then adjust the stat's tripping point depending on where it's positioned - almost certainly lower if it's sitting on a low surface. Basically, you set it to give your sitting room the comfort you want, and then you tweak every other rad in the house to provide what these rooms want.
     
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