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    • CommentAuthorandyman99
    • CommentTimeJan 7th 2018
     
    I've just moved into a new bungalow. Very leaky 1960's bungalow, so plenty to do. Initially noticed strange behaviour with the CH/HW. A new boiler was been installed last year, a Grant Vortex Eco - sounds grand. Looking at the plumbing, there are 2 separate pumps for CH and HW. No valves. There is one 22mm supply from the boiler that T's off to both pumps. All electrics go into a a chocbox type affair, not a proper Honeywell control box, so tracing them out is a little tricky, but I think I understand what is happening, see attached diagram (I hope).
    Its not a very satisfactory arrangement, as the boiler is activated by the HW On from the programmer until HW is up to temperature and then C1 brakes and C2 makes so the boiler is then activated by the CH On signal. This means that
    a) The HW pumps is always running
    b) If the HW is not up to temp, then the CH On signal never reached the boiler.

    Any ideas on how to improve this? Seems the switched CH/HW signals need to go through a logic OR gate?

    Long term I hope to replace the rads with UFH.
      Boiler Schematics.jpg
    • CommentAuthorSimon Still
    • CommentTimeJan 7th 2018 edited
     
    Unless I'm mis-understanding this seems OK to me. When HW is on (as set by the timer) hot water is prioritised over heating until the water store is up to temperature. Once the water store is hot heating activates.

    Since the boiler won't take long to heat up the water tank (maybe an hour if completely empty but that's unusual so usually much less) the radiators wouldn't even have cooled much in that time.

    That's the same way that my storage combi works - the UFH pumps switch off when it's heating water.

    The only thing I don't understand is you say its a problem that the HW pump is constantly running but also that C1 breaks when water is up to temp (and then pump stops). If you're waking up to cold radiators just set the timers so that the heating comes on an hour before the water.
    •  
      CommentAuthordjh
    • CommentTimeJan 7th 2018
     
    It's almost what is called a 'hot water priority' system but there are two problems as Andy says.

    1) The DHW pump runs whenever the boiler does. Including when the DHW is up to temperature and also even when the programmer says hot water should be OFF. That's not a total disaster but it does result in a lot more wear on the DHW pump and extra losses and perhaps noise from the pipework.

    2) If the DHW is not up to temperature and the programmer says hot water should not be heated, then there's no way for the CH circuit's call for heat to reach the boiler. Again, it's not a total diaster but it means that the DHW has to be programmed on whenever the CH is, instead of perhaps once or twice a day. Again extra wear and losses are the result.

    As Andy says, a logical OR seems to be needed. Maybe isolate the boiler from the HW pump, and put two NO relays in with permanent live to one contact of each and the other contact of each connected to the boiler. One coil powered from the DHW pump circuit and the other from the CH pump circuit. I think that would work but maybe there's a neater solution or maybe a different way that is both conventional and familiar to plumbers.
    • CommentAuthorandyman99
    • CommentTimeJan 7th 2018
     
    >djh, yes explained better than I managed. Associated issue is that the supply from the boiler is only 22mm. This appears to be correct in that the o/p from the boiler is only 22mm. My old house had a larger 28mm connection up to the diverter valve and then 22mm out to the radiators. Since this is only 22mm and half the flow is wasted through the continually running HW pump, I wonder if enough flow is going to the CH system. It does take a long time to heat the rads, however I strongly suspect some other issues at play, primarily that the pipes running under the suspended wooden floor are not insulated (/properly..). I'm desperate to have a look but the weather is against lifting floor boards atm, and there are 1001 other less interesting jobs associated with moving house to do. Also noticed what appears to be an inline valve on the HW circuit, at the o/p of the coil. Wonder if this could be used to restrict flow to this circuit? It appears to be in a closed position (though presumably it can't actually be fully closeable?)
    •  
      CommentAuthordjh
    • CommentTimeJan 7th 2018
     
    Posted By: andyman99Also noticed what appears to be an inline valve on the HW circuit, at the o/p of the coil. Wonder if this could be used to restrict flow to this circuit? It appears to be in a closed position (though presumably it can't actually be fully closeable?)

    Are you sure it's a control valve rather than a one-way valve or a drain or something? It would seem to be easier to restrict the flow by turning the speed of the pump down.
    • CommentAuthorandyman99
    • CommentTimeJan 7th 2018 edited
     
    Not sure exactly what it is, but here's a picture, its the vertical one with the adjustment slot in the horizontal position. I should have looked more closely as I now realise there is also a gate valve in the circuit. The pump is just to the left of the GV, which is a solitary valve, the pump has additional inline isolating valves so it can be removed. Maybe the GateValve is used to control flow? Or maybe is just left over from a previous existence, its a little messy in there.
      Valve.JPG
    • CommentAuthortony
    • CommentTimeJan 7th 2018
     
    Non return valve
  1.  
    Sorry Tony, it looks more like an isolation ball valve that you would normally find e.g. either side of a pump to enable the pump to be changed without draining the system. In the position shown (slot horizontal) it would be shut off. (and yes after a time they do leak a bit around the operating screw as noticeable in the photo)

    If it is a NRV there will be an arrow stamped on it indicating the direction of flow.
    • CommentAuthortony
    • CommentTimeJan 7th 2018
     
    Agree, sorry,
    • CommentAuthorandyman99
    • CommentTimeJan 8th 2018
     
    Thanks all. I agree it looks to be in the closed position, but it can't be, it is inline in the HW circuit. Its impossible to get a clear picture of the whole area though, so I will draw a schematic tonight. The pump has its own isolation valves, but difficult to photo, the gate valve is a solitary extra valve and whatever the vertical valve is, its yet another device between the HW coil and the boiler. Still wondering if there is a better way to control this system? It must be possible to disable the HW pump once the HW is up to temp? I'm also not sure why there are 2 pumps anyway. Its a basic bungalow with pretty short runs to everything. Possibly a legacy issue may be the HW was originally gravity fed and this was the "easiest" way to modify.
  2.  
    Sorry - I misread your circuit diagram yesterday so my reply is obviously wrong.
    • CommentAuthorandyman99
    • CommentTimeJan 8th 2018
     
    >Simon, thanks for taking the time to reply!

    This is my take on the plumbing - not sure it sheds much more light on things. The HW pump has valves either side and then there is the further gate valve shown in the photo and then the "Other Valve" that appears to be in the closed position. One thing I have noticed is two 15mm pipes (A and B in diagram) that T directly off the flow and return pipes. These disappear under the floor but are suspiciously close to a towel rail in the bathroom. The towel rail lockshield valve was completely open, which seems to be a bit of an easy path for water to take, so I have closed this down. Will do some more tests from cold tomorrow.
      Plumbing.jpg
    • CommentAuthorandyman99
    • CommentTimeJan 9th 2018 edited
     
    >djh - I think a pair of relays is the only way. I can't see anything specifically designed for this situation. Would you think this suitable?

    https://www.rselectricalsupplies.co.uk/chint-nch8-modular-contactor-nch820-240v_8443?gclid=Cj0KCQiA7dHSBRDEARIsAJhAHwiWnIGq42Z4AC78JyUHOyxuk8eCiSHugw8TVZrE8MHusFbx7fEMr7UaAiawEALw_wcB
    • CommentAuthorsnyggapa
    • CommentTimeJan 9th 2018
     
    Towel rail seems like a possible "always open" circuit that has to be available if you have thermostatic values on the other rads and they all close - that way you have a completely closed circuit, a pump trying to bust it open and a boiler trying to put 30kW of heat into a static pipe.

    I think that every heating circuit should always have a permanently open loop to allow for this, so be careful shutting off the towel rail

    -Steve
  3.  
    Posted By: andyman99'm also not sure why there are 2 pumps anyway. Its a basic bungalow with pretty short runs to everything. Possibly a legacy issue

    2 pumps avoids the need for a motorised valve to prioritise between DHW and CH. With 2 pumps you need NRVs on each circuit.
    To stop the DHW pump running permanently and to avoid back circuits then

    Posted By: andyman99I think a pair of relays is the only way.

    (The relays function a bit like the NRVs on the plumbing !!!)
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2018
     
    That relay looks to have plenty of capacity, but I am not an electrician, especially a qualified one, so I'd check with somebody who is.
  4.  
    Yup that relay is over kill at 20A. CH pumps even the old ones don't draw more that 0.5A. and modern ones considerably less
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2018
     
    Posted By: Peter_in_HungaryYup that relay is over kill at 20A. CH pumps even the old ones don't draw more that 0.5A. and modern ones considerably less

    The proposal is to connect the relay contacts to the boiler, not the pumps. But I agree that 20 A is overkill. Not that that's a problem in itself.
    • CommentAuthorCWatters
    • CommentTimeJan 10th 2018
     
    Do CH/HW pumps have a high starting current or behave like inductive loads?
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2018
     
    Posted By: CWattersDo CH/HW pumps have a high starting current or behave like inductive loads?

    Why does that matter?
    • CommentAuthorCWatters
    • CommentTimeJan 11th 2018
     
    Well if they draw 10A on start up then perhaps a 20A relay isn't such a bad idea.
    •  
      CommentAuthordjh
    • CommentTimeJan 12th 2018
     
    Since the pumps aren't connected to the relays, their current consumption is not relevant to the relay's rating.
    • CommentAuthorandyman99
    • CommentTime1 day ago
     
    Just for completion and thanks, final diagram and photo. Works fine, but still some work to do on pipe runs, which are all under a suspended wooden floor and mostly uninsulated
      picure_relays.jpg
    • CommentAuthorandyman99
    • CommentTime1 day ago edited
     
    Diagram, still learning sketchup!
      CH Wiring Modified.jpg
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