Central Heating Programmer query

Discussion in 'Electricians' Talk' started by johnjordan, Oct 30, 2021.

  1. johnjordan

    johnjordan New Member

    Are these electronic 2 channel programmers capable of controlling a oil boiler/pump directly, ie. not using a valve on the DHW?
    What i trying to find out is if the switching current capacity of a programmer rated 3(1)A will operate a oil boiler/pump with no motorised valve fitted on the DHW.
    There is a valve fitted on the CH side and will be wired as normal.
    5 wire valve is not available in danfoss

    The switch wire from the cylinder stat would be connected to the orange of the rads valve and to the boiler/pump
    If the CH was ON, there would be a backfeed through to the cylinder stat and if that was closed would go back to the programmer. Don't think this would be an issue though!

    Was trying to upload a wiring sketch but unable to do so
    Thanks
     
    Last edited: Oct 30, 2021
  2. The Happy Builder

    The Happy Builder Screwfix Select

  3. johnjordan

    johnjordan New Member

    Yeah, but the way it is the pump will be coming on with the burner when HW switched on.
    There is a valve fitted on the CH pipework, the plumber has not fitted a valve on the DHW as he has no space!
    Told me to wire it in as normal but leave it hanging there....not connected to anything mechanically.
    Can i wire it so the HW is connected to burner/pump directly? As well as the orange sw from CH valve.
    Think its a bit of a waste just leaving a valve hanging doing nothing really.
    Thanks
    Sorry about the terrible explaination!
     
  4. The Happy Builder

    The Happy Builder Screwfix Select

    It sounds like you need a programmer with a gravity hot water setting, so that it turns the hot water on along with the central heating.

    This is not the best of setups, but it sounds like you may have to work with what the have got. You will probably have to spend some time researching and working out what to do for the best.

    This programmer has a switch on the back of it that you use when installing it to tell the programmer to turn the hot water on with the heating, see the diagram on page three.

    https://www.draytoncontrols.co.uk/sites/default/files/LP822 (U&I Guide).pdf
     
  5. johnjordan

    johnjordan New Member

    I think the HW will be on with the CH anyhow, as there is no valve on the DHW circuit.
    Plumber left Danfoss 2 channel programmer
    Wish i could post a drawing of my intended wiring, but can't seem to do so. 'file is too large' or 'security error' comes up when i try to upload a picture
     
  6. MGW

    MGW Screwfix Select

    Yes I have an oil boiler on a C plan working with Nest Gen 3. OK a little more complex in my case, but this plan C-Plan_basic_Nest.jpg will work, Hive has a much simpler method, it is done in the software, so one output to pump and one to boiler and it works out internally when to switch on just boiler or boiler and pump.

    But that does not mean all will work, note with Nest using the com of volt free contacts to feed boiler, and both N/O and N/C contracts used, some thermostats do not have volt free and the com is internally connected, as with Hive, so unless software allows setting for C plan then it will not work.
     
  7. The Happy Builder

    The Happy Builder Screwfix Select

  8. The Happy Builder

    The Happy Builder Screwfix Select

    The convention is that in wiring diagrams the relays are shown relaxed in the off position, so the diagram that @MGW posted shows the system when it’s turned off.

    In that diagram the pump doesn’t come on for the hot water, just the boiler, so you may need to wire the pump to the boiler so it runs whenever the boiler is on.
     
  9. MGW

    MGW Screwfix Select

    Some it is a simple set of DIP switches upload_2021-10-30_13-59-0.png some have different versions upload_2021-10-30_14-0-45.png upload_2021-10-30_14-1-48.png and
    I missed that, I would have thought if there is an orange wire then it is a Y plan? If that is the case then what I have said does not apply.
     
  10. MGW

    MGW Screwfix Select

    Y plan Y-Plan.jpg C plan three versions C-Plan_old2.jpg is simple original version, there was a second version which allowed it to be left on DWH in summer C-Plan_old.jpg and a version with a motorised valve in the DHW C-Plan.jpg the latter is often not advised with oil as often no cooling down cycle. Many of the new combined thermostats and programmers have option for the very old system which is called gravity, but one has to be careful as often the latter C plans will not work.
     
  11. johnjordan

    johnjordan New Member

    No, its not a y plan, as that's a 3 port valve set up.
    What i have is a 2 port valve on CH,
    I think its mean't to be S plan, but the plumber can't fit the DHW valve to the pipework.
    Think its not a great job really, but have to wire it some way.
     
  12. MGW

    MGW Screwfix Select

    I have re-read posts, and not sure if really using gravity system, the idea was with gravity system not to run pump if only DHW required, but I found in my house radiators would also heat with thermal syphon, specially on the third floor, also if pump ran for even a minute once it started it would continue to heat with just thermal syphon, so I had to fit motorised valves to the central heating.

    In theory with TRV heads should not be required, and now I have electronic heads that may be true, but the old mechanical head set to 2.5 starts to close at around 18 degs C but does not fully close until around 23 degs C, so although radiators not very hot, they are not cold.

    However my system is a C plan with a motorised valve on the central heating. Some thing like this C_Plan_My_HouseD.jpg I made a mistake, at 70 my logic skills were not as good as they were, since using two pumps it needed relays, this C_Plan_My_House_single_pump.jpg would have been so much easier with one pump. Why plumber fitted two pumps I don't know, house three levels the lower level rarely used has be converted into a flat, and when I bought the house to get central heating to work in main house I had to go outside down a set of steps into the flat and plug in the second pump.

    Reason for Nest Gen 3 was only two wires between main house and flat, and with Nest Gen 3 those two wires take the command information and keep back-up battery charged in thermostat. It was not got because of Geofencing or ability to switch on/off with phone.

    It was not as good as expected, as when google took over Nest they removed support for the Energenie TRV heads, in USA they have released a remote sensor which does same job, but has not been released in UK yet.
     
  13. johnjordan

    johnjordan New Member

    This was the way i was going to wire it.
    nb. room stat omitted
     

    Attached Files:

  14. johnjordan

    johnjordan New Member

    how can i put a picture up? Uploading photo doesn't work. Uploading scanned image is pdf
     
  15. johnjordan

    johnjordan New Member

    can i connect the sw wire from the cylinder stat, orange wire of CH valve, burner and pump together?
    If hw is switched on at programmer, cyl stat closed, boiler and pump will operate, CH valve will be closed.
    If ch is switched on at programmer, room stat is closed, valve is energised closing the volt free contact within and energise the boiler and pump.
     
  16. The Happy Builder

    The Happy Builder Screwfix Select

    I think that sounds right.

    Normally the two port valves are used to prevent the electric back feeding the part that is supposed to be turned off. But here the hot water will never be turned off whilst the boiler is running.

    You are going to end up burning more oil than you need to, because there’s not a two port valve on the hot water side. But if the cylinder is in the middle of the house and any heat that escapes heats the interior of the house it’s not really going to waste, if however the radiator temperature is higher than you want the hot water the water will carry on heating up after the cylinder stat has shut off.
     
  17. adgjl

    adgjl Active Member

    The best option is to get the plumber back to do their job properly and fit the second valve . . . or find another plumber who will.
     
  18. johnjordan

    johnjordan New Member

    Thanks. Yeah, the cylinder stat is going to be ineffective in controlling the cylinder temp whe runing the CH.
    Did you open my wiring diagram pdf a few posts up?
    Is it ok to control the boiler/pump directly via the cylinder stat as opposed to fitting a 'dummy' dhw valve as plumber suggested?
    The current ratings on the programmer internal switching is low 3(1)A where 3 is resistive load and 1 inductive. Pump and boiler would be inductive loads i think.
     
  19. johnjordan

    johnjordan New Member

    Yeah, i know that!
     
  20. The Happy Builder

    The Happy Builder Screwfix Select

    Gas boilers are normally fused at 3 amps in the SFCU and oil at 5 amps, but I have never actually measured the current of either as I said in another post about a room thermostat a few nights ago.
     

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