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Vitodens 100-W WB1B temp won't go over 70C

Discussion in 'Plumbing and Central Heating' started by Kris Zylek, 27 Dec 2019.

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  1. Kris Zylek

    Kris Zylek

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    Hi All,

    I have a Vitodens 100-W WB1B boiler feeding an 8 rad system. There are 6 rads on the ground floor (4 steel and 2 cast iron) and 2 rads on the lower ground (vertical ones). The boiler must be a few years old but the rads are new and I sized them as best I could using the BTU calculators across various websites. We just moved into the property so I have no clue about how good/bad the old panel style radiators were.

    Since Day 1, no matter what the dial is set to on the Boiler for heat (the dot point between 4-5 or higher), the boiler temp never reads above 70C. The Burner output shows 1 bar and the flame seems to be on all the time. I also got the plumber to install a Nest thermostat and it never gets to my target temp of 20C. The max value I see is 18C. As an example, 1 hr before I came home, the temp was 14C and the boiler was off. I started it and now 7 hours later, it's still only 18C.

    The rads range from warm to hot but barring the cast iron rads, none of the others seem too hot to touch for long periods of time. My question is - is there something wrong with the boiler and what can I test/check?

    Any help/direction appreciated.
     
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  3. smarriott

    smarriott

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    Hi

    Did you every resolve this, sounds like I have the same issue. Boiler over modulating and not consistantly heating the house or hot water.

    Cheers
     
  4. ericmark

    ericmark

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    Odd no answers nearly a year ago, but in the main it is balancing of the lock shield valves. The boiler measures the return temperature and adjusts output to ensure that return temperature is within limits to gain the latent heat.

    Looking at around 15°C drop across the radiator, but until resent I did not have a thermometer to measure the differential, so I used following method.
    Starting at closest radiator to boiler, i.e. one which would normally heat up first, likely up stairs as heat raises, turn off the lock shield valve fully, wait for pipes to cool, then turn on ¼ turn at a time with a few minutes between each adjustment, until one pipe gets warm.

    Repeat this on all other radiators slowly working away from the boiler, you may need some further tweaking latter but this will ensure the return water is not too hot.
     
  5. ericmark

    ericmark

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    What happens is while the heating is running the TRV heads modulate the flow, so each radiator gets its fair share, but once it stops, on re-starting the closest radiator gets it first and returns hot water to boiler so the boiler modulates, i.e. flame height turns down. Once the TRV starts to close, then the water goes to next and room by room it will heat up in fullness of time, but with the boiler giving out maybe 6 kW instead of 28 kW it takes a long time.

    The in real terms the setting of the lock shield valve only matters for a re-heat, once all rooms hot it does not matter as much.

    However the TRV takes time to open and close, so if the lock shield is open too wide, the TRV can't close fast enough, so the room temperature over shoots, so you get a sine wave of temperature, or hysteresis where the TRV is over shooting in both directions.

    So if the TRV is set to 20°C and after some time the room has not reached 20°C you open the lock shield a little, and if the temperature over shoots, you close the lock shield a little, easy for me, my TRV's show the temperatures in °C TRV_report.jpg so I know exactly what the TRV is set to, but the old TRV's which don't connect to PC tend to have some thing like *123456 and some where between 3 and 4 is around 20°C so your left with two devices, the lock shield valve and TRV and not a clue which one needs adjusting.
     
  6. ianmcd

    ianmcd

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    you would be better starting your own fresh post if you want the correct advice
     
  7. Kris Zylek

    Kris Zylek

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    I managed to improve the situation but it took a lot of trial and error.

    1. As the earlier posters said, the system wasn't balanced to start with. So I went around and balanced all the rads so I had approx 11 C drop across each one.
    2. There was a lot of gunk in my CH, so I had to run Sentinel X400 / X800 a couple of times and flush each rad 1 by 1 to get all that sludge out and improve circulation.
    3. The humidity in my house ranged between 50-70% so I got a dehumidifier to keep it below 60% which helped make the house feel warmer.
    4. Being an old house, there was a lot of heat loss due to gaps around windows. I sealed those using tesa moll strips and also applied thermo cover on the single glazed windows and it helped retain heat better.
    5. In my case the plumber had put the TRV and LSV the wrong way around on a few rads. It took balancing the rads to bring this to light and still get a reasonable drop on the rad.

    I can get the house up to 21C even if its -1 outside. The gas use is same as before but I get more out of it, probably due to less wastage. The house doesn't heat up super quick but since we're WFH due to the current situation I don't let it drop below 19C and it seems to work out ok.
     
  8. DIYnot Local

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