2 Room Thermostats work, the third seems to operate differently

Discussion in 'Electricians' Talk' started by ItWasAPub, Nov 12, 2013.

  1. ItWasAPub

    ItWasAPub New Member

    I am not an electrician but am quite good with electrics and wanted some advice before calling out an electrician to work out what is wrong with our room thermostat.

    I have a Main HE Condensing Boiler and three room thermostats that operate different parts of the house, which has been extended a few times. There is also a Drayton Lifestyle LP722 dual channel programmer for hot water and heating next to the boiler. Two of the heating thermostats work perfectly, i.e. when the timer on the LP722 is off for heating the thermostats have no effect. The third thermostat works differently. It comes on during the night (sometime after 3am) and during the afternoon (just before 4pm) if the temperature dial is low enough for it to come on. I am wondering how this can be. The heating and hot water are off between 11pm and 5:50am, so it seems this has no effect on the third thermostat. All three thermostats are of the old fashioned type, turning a dial to the desired temperature. The third thermostat is a Honeywell 4200 (looks quite old).

    I would really appreciate if anyone could help in telling me why the third thermostat can operate in this way.
  2. wally

    wally Screwfix Select

    I could understand it if the third stat was a programmable one but you say its an old stat & I can't find any reference to the number you gave
  3. "It comes on during the night (sometime after 3am) and during the afternoon (just before 4pm) if the temperature dial is low enough for it to come on."

    I take it the house isn't used during the day, so no heating is on? In which case these two times roughly correspond to when the house has dropped to its coldest temp (temp falls during the night after the house has been heated in the eve - so 3am won't be a surprise. Ditto 4pm - the sun has passed by the window and is beginning to sink - temp drops.)

    Tonight, after 11pm when the timer has gone 'off', turn the 4200 stat down until it 'clicks'. Does the boiler come on?

    If 'yes', then clearly that 'stat ain't wired via the timer, just permanently live.

    Solution - and you'll love me for it - is to replace it with a programmable 'stat. That zone will now work completely independently of the others; both timings AND temps will do exactly what you've programmed it to do.

    (Later on, you'll change the other two too. And just switch your timer to CH 'on' 24hrs...)
  4. electrograph

    electrograph Member

    Generally, when a 'stat works independently of the time control, it is there for frost protection for a boiler or for pipework installed in an otherwise cold part of the house, e.g. an attic or attached garage. Such a 'stat would normally be preset at around five degrees and on older types the dial would be removed to prevent interference with that setting.
    A frost 'stat is usually wired directly to the fused spur so that it can deliberately by-pass the time control -it is very often accompanied by a pipe-'stat strapped to the return pipe to the boiler.
  5. electrograph

    electrograph Member

    Oh, and Good evening Dev's ^. Thank you so much for that e-mail you sent me when I was rather poorly all those months ago. It was very much appreciated, as was the one from Tompus, too........
  6. Wha...? You mean? It's... It's... You...are...?



    Is it you? :D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D?
  7. ItWasAPub

    ItWasAPub New Member

    Thanks for the responses so far.

    The house is used during the day and the heating goes on in the other parts of the house without problem. This third stat controls two bedrooms and a bathroom.

    >>"Tonight, after 11pm when the timer has gone 'off', turn the 4200 stat down until it 'clicks'. Does the boiler come on? "
    It seems a plan, so I will try this tonight and try some more investigation.
  8. Lectrician

    Lectrician Screwfix Select

    Some older multi zone systems used to have a "set back" stat. When the heating is off, this stat would take over and maintain a minimum set back temperature. Similar to a frost stat, but designed for comfort. This was prior to programmable stats being available.
  9. ItWasAPub

    ItWasAPub New Member

    This does come on when the heating is off. Also, it doesn't come on when the LP722 timer is on for heating. If I simply replace this with a new programmable room thermostat, will that be all that I need to do? May it be necessary to reconnect to the boiler?

  10. Lectrician

    Lectrician Screwfix Select

    You have three room stats - Do you know for sure what area/zone each controls? Does it definitely control a separate area? Do you have three separate zone valves in the plumbing somewhere?
  11. IWAP, IF this stat makes these few rads only come on and off regardless of what the LP722 timer says, then it can surely only be a matter of replacing it with a prog-stat.

    Just make sure that it's not as Lec says - best to carry out his checks first; that each stat controls a separate zone, and that's all.

    You should also check that the 'live' wire inside that stat goes dead when the 'master' CH switch is turned off. Is there a fused-switch somewhere near the boiler that powers everything? Then make sure this weird stat also goes dead with everything else. Very naughty if it doesn't.
  12. ItWasAPub

    ItWasAPub New Member

    One thermostat is for downstairs, one for the existing upstairs and the other for the upstairs extension, and it is this one that has the problems. I can see three separate zone valves and have attached pictures of the thermostat and zone valves.

    I will replace this thermostat with a programmable one and check all wires go dead.

    Thanks so much.

    Attached Files:

  13. Lectrician

    Lectrician Screwfix Select

    Three zone valves, and you should be able to see the little flag on those zone valves move when the stats (and time clock) call for heat. The little manual lever flag will have spring pressure behind it when closed, but will be loose and floppy when open. You can then tell which stat is controlling which valve.

    Assuming this stat does control a valve, regardless of the time control, then you can swap it for a programmable stat, or alter the wiring to have it controlled via the existing time clock. But as said above - make sure it is wired as part of the central heating system, and not as some random add on from a separate source.
  14. Looks ideal, IWaP.

    In fact, you may end up wanting to swap all three 'stats for prog types. If the upstairs is mainly the sleeping quarters, for instance, then you'll only want that coming on for an hour before wakie, and an hour before sleepy. And you can set the prog stat to do that automatically, and - say - prevent it falling below, say, 14oC through the night.

    They're grrreeaaattt!
  15. ItWasAPub

    ItWasAPub New Member

    I replaced the Honeywell stat for a programmable one and I have wired this in correctly. The radiators in this zone still only come on at 3:50 pm and probably around 3:50 am for a couple of hours each time. If I lower the temperature on the new stat then the radiators will go off between 3:50 and 5:50pm and if I raise the temperature they will go on again during this time period. Outside of the two periods the stat seems to have no influence. The wire to the stat disappears in to the wall. Any ideas where else I can look to see where these radiators are limited to 2 hours in the afternoon and two hours in the early morning? I am baffled. Once I have the problem fixed I will be replacing the other two stats as suggested.
  16. daver34

    daver34 Member

    Does that stat control/open and close valve , turn stat on to call for heat(put timeclock c/heat temporarily to on allday) - does valve lever move freely, turn stat off - does valve lever now have resistance(spring-can be moved manually)

    With new stat turned off, turn stat that operates upstairs c/heat on, does ext c/heat rads warm up.

    Why was an old stat controlling new ext c/heating?, did the ext heating ever operate properly before.

    Your new prog stat wiring will have to be altered, if it was wired correctly before, then the live to stat is actually a switch wire from the clock(on), this would have to be a perm live otherwise the existing timeclock can switch prog stat power off.

    Where in the house is the boiler?, could it have a frost stat - pipe stat set up?. Upload more photo`s showing boiler and all controls, so we can see all exposed wiring, if joint box/wiring centre take a pic of connections.

    Does the boiler have inbuilt frost protection?(make/model).
    Last edited: Nov 16, 2013
  17. unphased

    unphased Screwfix Select

    I have theory that you may wish to investigate. The thermostat which operates independently of the Drayton Programmer must have a switched live feed to it separate to the Drayton. Because you have said the heating for this area operates at fixed periods each day it has to be wired to another timer, that is operating independently of the Drayton Programmer. It is pointless installing a programmable room stat to replace the existing room stat because the separate timer is controlling it. No point having two as one will override the other. See if you can find another timer, maybe close to and connected to the zone valve that is operating. This has to be the reason.
  18. IWaP, have you actually tried what I suggested up there^?

    "Tonight, after 11pm when the timer has gone 'off', turn the 4200 stat down until it 'clicks'. Does the boiler come on? "
    It seems a plan, so I will try this tonight and try some more investigation.

    I'm not sure if you have replied to that properly.

    IF you turn the 4200 stat (ok, long gorn...) down at, say, 11pm at night AFTER your LP722 has turned its CH off, AND that 3rd zone's rads COME ON, then - surely - that stat is being supplied by permanent mains power so is working COMPLETELY independently of the LP722 and other stats?

    Did you try that first?
  19. Or, take your new prog stat off its back-plate and test for 'live' feed both before and after 11pm (when the LP722 goes off).

    What temp is your new prog stat set to that makes it come in the afa and during the night?
  20. unphased

    unphased Screwfix Select

    DA I am convinced that the third room stat is being fed from a timer set to 3am and 4.00pm for a couple hours, that is separate to the programmer, sending a live feed to this stat which is in turn wired directly to the boiler or orange wire on the wiring centre. There can be no other explanation.

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