Boiler Overheating / Pipes extremely hot

Discussion in 'Plumbing and Central Heating' started by liddc, 20 Oct 2017.

  1. liddc

    liddc

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    Hi,

    First post so apologies if I miss anything out!

    I moved into a house around 5 years ago (UK) with a standard gravity fed Central heating System connected to a Sunier Duval Xeon 50ff boiler. In the airing cupboard there are two zone valves and a Pump and in the loft two expansion tanks one for the hot water tank and one for the C/H.

    When I moved into the house all radiators were replaced and a lot of thick black sludge came out however since that time the system has been drained and inhibitor added, the last time I did it about 3 years ago the water was perfectly clear.

    For awhile I've had a problem with the boiler kettling i.e. lots of gurgling coming from the boiler and pipes. After a few minutes the boiler will switch off then continue this cycle until the tank and room thermostats reach their set temps. All four pipes connected to the top of the boiler are extremely hot as are the radiators and pump. (Too hot to touch without getting burnt).

    Things I have checked :

    • Zone valves - They appear to be working as when the system is powered off if I move the leavers to "open" they move back to auto with a motorised sound.
    • Pump - Spins freely when powered off using the screw in the middle and not running dry as water comes out. If I put my ear to it, it does sound "gritty" when powered on but I can feel it vibrating so it appears to be working. I would mention however that it does seem quieter overall than when I first moved in even on the highest setting of 3.
    • Boiler thermostat is set to half way I also moved it as close to minimum as possible. All four pipes coming in and out of the boiler are very hot i.e. close to boiling all of the time.
    Even though it appears the boiler is overheating I never have to press the overheat reset button and it fires up every time to continue heating the water, so to me it appears an internal sensor is picking up that the water has reached the boilers max temp of 82.C and then waits for it to cool down again before carrying on the heating process.

    Not knowing much about boilers or central heating systems but having done quite a lot of reading on these forums, my suspicion is that either the boiler thermostat is faulty or there is a problems somewhere else in the system.

    Is it possible that the boiler isn't getting a cold water feed or if the pump is too clogged with sludge would this cause the water in the system to get too hot due to lack of circulation?

    Alternately if the boiler heat exchanger is clogged up would this cause it to overheat the water as much as it is doing?

    Any suggestions / advice would be appreciated before I call out a plumber.

    Thanks
     
    Last edited: 20 Oct 2017
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  3. liddc

    liddc

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    Update : I just ran the system again for about 10-15 minutes with both CH and HOT Water turned on via the programmer and there was no kettling. The pump was still running very hot but two of the pipes coming into the boiler on the right remained at a fairly low temperature.

    As soon as a switched off the CH heating via the programmer (so the boiler was just heating the water in the tank) the gurgling started straight away and the two pipes on the top right of the boiler got extremely hot again. I went to the airing cupboard and manually opened the zone valve for the radiators and the pitch of the pump changed and I think if I had left it that way I the kettling would have stopped again.

    The zone valve that remained open did seem to be making a bit of a vibrating noise once the other switched back to auto but the pipes above and below it were hot meaning it must not be closed.

    When I had a plumber out a few years ago he said that when I had the central heating on I had to have the hot water turned on via the programmer. Should both need to be turned on all of the time in this setup?

    Thanks
     
    Last edited: 20 Oct 2017
  4. ianmcd

    ianmcd

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    you have a fully pumped open vent system not a gravity system they are two different things.
    Not with 2 zone valves you dont you can have both or either independently of each other.What programmer do you have.
     
  5. liddc

    liddc

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    Thanks for the reply and clarification about the system :)

    The programmer is a SIEMENS - RWB29 fitted when I moved into the house 5 years ago.

    I also put in a new Honeywell room and Hot Water tank thermostat at the same time, the tank thermostat is always set to 50.C
     
  6. ianmcd

    ianmcd

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    Check on the boiler wiring panel (turn power off first) and look and see if there is a red link installed between SL and 9, in fact if you can take a pic and post it of the boiler wiring
     
  7. liddc

    liddc

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    Thanks again for the reply.

    Unfortunately the tiler decided to seal in the programmer with grout when he did the kitchen but after breaking some of the tiling away underneath to get at the screws I managed to take this photo looking up at the wiring from the bottom of the programmer.

    Sorry it's not great but from the wiring diagrams I found online it seems to be correct?

    N L 1 2 3 4

    IMG_20171020_193525873[1].jpg
     
    Last edited: 20 Oct 2017
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  9. ianmcd

    ianmcd

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    I meant the wiring panel on the boiler itself, with your installer saying you have to have HW and CH together, I am wondering if the Gravity hot water link has been left in.
     
  10. liddc

    liddc

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    Ah ok sorry picture of the boiler wiring below.

    Also I tried to turn the CH on without the HW and it wouldn't fire up so the programmer must need both to be on for CH to work but HW will work albiet with the problems described in the original post.
     

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    Last edited: 20 Oct 2017
  11. ianmcd

    ianmcd

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    OK it is as I suspected your boiler is wired wrong, if you have 2x 2port valves then the pump has to be wired into the boiler and That red link needs to be removed and your external controls wired through there, I think you might need a proper engineer as I think the rest of your wiring is slightly wrong too, but your boiler id defiantely wrong and that is why the water is getting too hot, @stem might be able to run through how to wire your external controls in correctly, he has a lot more patience than me
     
  12. liddc

    liddc

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    Hi Ian, Thanks again for all your help with this. I definitely don't want to be changing any of the internal boiler wiring myself so I will get an engineer in ASAP and I'll have them check the external wiring at the same time, hopefully I will be able to get the panel open without removing any tiles :)
     
    Last edited: 20 Oct 2017
  13. ianmcd

    ianmcd

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    it could just be connecting the two orange and two grey wires from the zone valves into the terminals when you remove the red link, but you must get the pump wired direct from the boiler for your system as that controls the pump over run , you dont need that on a gravity hot water system, make sure you ask when you call if they are familiar with wiring S plans systems
     
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