Working out what a pump does.

Discussion in 'Plumbers' Talk' started by MGW, Jun 5, 2019.

  1. MGW

    MGW Screwfix Select

    Oil fired central heating for main house, granny flat, and domestic hot water, [​IMG] main controller has option for hot water only, however seems still heats radiators, there is a thermostat [​IMG] in the granny flat that seems to control both main house and granny flat, and a unit [​IMG] which I think is some form of thermostat but no thermostat found in main house either for central heating or domestic hot water, and there are two pumps, one clearly supplies from a 13A socket with no connection to main controller or any other electrical component on the system. The other seems to only run when set for central heating.

    It would seem domestic hot water is thermo syphon.

    If the pump with 13A plug is running the bedroom radiators seem to warm up faster, but if not running they still warm up, switching to domestic hot water only the bedroom radiators take longer to warm up, but still warm up.

    Pipes are hidden, trying to work out what does what, but failing, any ideas why two pumps, or how that controller works please.
     
  2. heatyman

    heatyman Well-Known Member

    Your problem is probably due to thermosyphoning from the DHW return. To establish if this is so, from cold, turn on to HW only, and see whether the radiators heat from the flow or return. To establish which is flow and which is return, turn up the room thermostat on HW and CH selected. The flow will heat up first.
    Your picture of the 'unit' is not very clear. What is written on it?
     
  3. The Teach

    The Teach Screwfix Select

    Seems the heating installation is not a standard plan,who knows how well the system was initially installed and subsequently altered :(

    Tbh,re-piping & rewire the complete system to fully pumped with zone valves,room thermostats,cylinder stat,programmers etc (not smart controls) would be my only choice. Then you have a standard system which is guaranteed to work :).

    :)
     
  4. ajohn

    ajohn Screwfix Select

    Thermo syphon for hot water is a standard system but sound like this one doesn't work as it should. On the one I have had anything to do with the boiler is a metre or so away from the hot water tank. Effectively near a wall to an airling cupboard that has the water tank in it. The pump, only on when heating is required is adjacent to the boiler in one of the heating circuit pipes - the feed, There is several metres of pipe to the first radiator. The set up has been in a bungalow from new built in the 70's and much to my surprise works well. Only odd thing about it is not using the usual Gundfos pump that many Y plan systems use, different model.

    The C plan is similar, called gravity circulation for hot water. The hot water tank has a separate circuit with no pump, The central heating circuit has a pump This version does use a hot water cylinder thermostat. What I have called thermosyphon probably has a plan name as well - afraid I don't know which one. It's as old as the hills. The C plan is a modification that allowing different heating and hot water temperatures, the simplest one that can do that. Yours by the sound of it has the boiler thermostat setting both hot water and heating circuit temperature.

    Need a much better photo of the small unit but you mentioned that you thought that the granny flat was heated by the pump with a plug on it. Sounds like this can't work that well as an independent control of the heating to me as it would need a totally separate circuit in the boiler otherwise some flow would be likely to go into the house circuit. You could probably get round that by fitting a normally off motorised valve on the outlet to the pump wired to the pump power feed so that flow can only happen if that pump is running. However I'd assume that who ever did it thought that some heat going to the granny flat when just the house heating was on is ok so you may be looking at a problem that doesn't matter. They'd likely assume that if the house heating was on the granny flat would be too so that pump on. When it's off those radiators may not heat up anyway.

    You should still be able to fit thermostatic radiator valves unless you also have a rather early heating circuit where the radiators are all in series. Mostly used in commercial buildings with large cast iron radiators but might have found it's way into some houses but I would have thought very old ones when few could afford it.

    I managed to find one picture of the type of heating you seem to have but there are variations

    http://www.schoolphysics.co.uk/age1... heat energy/text/Hot_water_system/index.html

    John
    -
     
  5. heatyman

    heatyman Well-Known Member

    Thermo syphoning = gravity circulation. Gravity DHW was used a lot, and is relatively inefficient.Building regs have specified for many years that any significant alteration to a heating system should include full thermostatic control of the HW and CH. (i.e Y plan or S plan). On this system, there may be a time when heating is needed in the granny flat but not the main house, so separate zoning would enable this.
     
  6. MGW

    MGW Screwfix Select

    I have tested and it seems granny flat has a pump controlled by a thermostat, it is the main house which has a plug in pump, the timer/programmer it seems just switches on the heating and it does not matter if it says central heating or hot water it does the same, I think there was at some time a second thermostat for house, but now only the RF receiver remains there is no transmitter/thermostat for the house.

    Turning the plug in pump on seems to reverse the flow through radiators in the house and make them heat up quicker, however even if not turned on, the house radiators still get hot, there is no way to heat the domestic hot water without heating the house.

    Plumber comes today, either motorised valves or check valve/non return valves are clearly required. Also a tank thermostat. He is also involved with repairing floor so may be able to fit cables.

    I am not worried about wiring, as long as valves and cables are in place, however it may need some relays if using only pump, as three functions all need to run boiler but not each other.
     

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