Combi boiler cutting in and out

Discussion in 'Plumbers' Talk' started by Silver45, Mar 22, 2020.

  1. Silver45

    Silver45 New Member

    Pump wasn’t running. Shall I try with it running?

    I think I’ve found the low water pressure switch at the back of the pump. It’s got a black and white wire going to it but this corresponds with my manual. See pics. Shall I open the box and link them 2 wires?

    All valves are open

    Thanks
     

    Attached Files:

  2. Silver45

    Silver45 New Member

    I’ve circled 2 parts on the attached pic.
    I believe the top one is the differential pressure switch part number 0005PRE11015/0.
    It looks like the lower part circled in the pic is the low water pressure switch that you suspect. From diagram it looks like they are wired together so shall I just join the 2 wires and bypass them both and run a test?

    Thanks
     

    Attached Files:

  3. Silver45

    Silver45 New Member

    There were 2 connectors on the back of the low water pressure switch. I took them off and connected together as suggested. Unfortunately no change. The pilot light display illumination still went off when heating demanded. Sorry for the confusion. My manual drawing showed the low water pressure switch to resemble the differential switch. Once I googled the parts I found photos.

    So I guess that switch is ok, any suggestions of where to look next?

    Thanks
     
  4. Silver45

    Silver45 New Member

    Anymore suggestions of where to look or test please?

    If there’s nothing else to test and it’s a blocked pipe issue as previously suggested, in the absence of a power flush or the ability to get someone in to do a flush is there any value of me trying to flush the pipes out with a garden hose to the bottom of various radiators in the system? I have pretty good mains water pressure.
    Obviously closing connectors at boiler so nothing flushing through boiler.

    Thanks
     
  5. Teki

    Teki Active Member

    Is the water from the radiator bleed valves brownish/black?
     
  6. Silver45

    Silver45 New Member

    No not from the bleed valves but it’s not long been completely drained and filled up with clean water
     
  7. Teki

    Teki Active Member

    Hope you added inhibitor?

    How old is the system? It does seem like a circulation problem. If there is a blockage, you can try narrowing it down by turning off all the radiator valves but one. If they aren't TRVs, remember the number of turns. Do not turn off the lockshield valves. Repeat for all radiators in turn.
     
  8. TheMorg

    TheMorg Active Member

    The pilot light is the burner light - if it's illuminated are you sure the boiler has not just modulated right down and is running on its lowest output rather than the boiler going out but the led stays lit(there's a sight glass to check).
     
  9. Silver45

    Silver45 New Member

    Yes I added inhibitor. The system was inherited with a house i bought. I don’t know the age or history. More radiators have been added within the last 2 years. It was heating fine before, it’s jist not working correctly now.
    The boiler could be modulated right down but I don’t think it is, it seems like a problem to me? I can feel the ch out pipe under the boiler go from hot to cold. It’s like the boiler fires up and comes on for 30 seconds then may go off for 2 minutes and then come back on for another 20-30 seconds and so on. I basically get a 20-30 second burst of hot water through the pipes every couple of minutes. It takes ages to get heat to the radiators although it does happen eventually.

    Does it sound like a blockage somewhere?

    I’m ready to drain the system and try and flush out the pipes from various radiator points with my garden hose if this is worth trying? I get 20 lpm of cold water pressure from my mains. Would this be worthwhile?

    If I’m going to attempt this some advice would be appreciated

    Thanks
     
  10. Silver45

    Silver45 New Member

    I done a makeshift flush with my mains water pressure and was able to get a lot of black **** out the system. I narrowed the worse area down to one radiator which happened to be the final rad in the chain before the pipes head back towards the boiler. I removed the rad and just linked the 2 pipes together. Straight away the boiler started working better. I don’t think it’s at full health but it’s so much better. I’ve added some fernox system cleaner and I’ll let that circulate for about a week and try again. I’ll just order a new radiator for the removed one. Once this lockdown is over I’ll get someone in to do a proper flush

    For anyone that contributed thanks for your efforts in helping me figure it out, it’s appreciated :)
     
  11. Teki

    Teki Active Member

    Add some Sentinel X400 to the system and let it circulate for 1-2 weeks then drain down. It will loosen any sludge and hold it in suspension until you drain the system. It may well save you having a full flush done.

    Do you have a magnetic/debris filter fitted to the system? If not, well worth having installed.
     
  12. Silver45

    Silver45 New Member

    Yes i have a magnaclean. That only collects the soft mud like sludge though, what I got out from my makeshift flush was hard black bits like tiny bits of coal.

    I had a 1/3rd bottle of x800, I’ve put that in for now. I’ll buy the correct amount of x400 for my system and put that in for 2 weeks while keep on checking and cleaning the magnaclean

    Thanks
     
  13. Teki

    Teki Active Member

    The advice I have been given from Sentinel and from personal experience, X800 is designed for use with a power flush machine. It doesn't loosen sludge as well as X400 if left to circulate in the system.
     
  14. Silver45

    Silver45 New Member

    Ok great. That’s really useful. Thanks

    It’s only as I had it, my system is 18 radiators so the 1/3 bottle I had won’t even touch it. I will order 2 bottles of x400
     

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