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Thread: Plumber can't fix two zone system - problem downstairs

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    Default Plumber can't fix two zone system - problem downstairs

    When the two zone system is set on the timer, I come in to find it warm upstairs but the downstairs radiators are completely cold. If I then turn the system off, wait half a minute, turn the downstairs zone on first and the upstairs zone on a couple of minutes later, everything is fine and the downstairs radiators warm up very quickly. The motorised valves and thermostats appear to be working fine. A plumber changed the pump and also drained the system, saying that he found some iron oxide in it. The pump sounds as though it is straining. Is there a blockage? If there is, why did it drain and why does it heat up so quickly. I have a bill for over 400 and we seem no nearer to solving the problem!

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    Moderator toscal's Avatar
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    Default Re: Plumber can't fix two zone system - problem downstairs

    If the zones work separately, then it could be the the valve that allows for both to come on, or if its via two valves, then it may the order in which these come on.
    What happens if you turn half of the radiators off upstairs when both zones are on.
    You say that when you switch it all off, then downstairs on first then upstairs it all works. May be when the timer switches both it switches upstairs on first then downstairs, can you change the zones round on the timer to see if that helps.
    It could be the pump is not large enough. Don't know if you can do this with this type of system. But can you fit another pump so each zone is pumped independently of each other. It just an idea and I don't know if it would work.
    Hope some of these ideas help.

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    Default Re: Plumber can't fix two zone system - problem downstairs

    Thanks for the suggestions. I tried turning off most of the upstairs radiators last night. When I woke this morning, all the radiators were cold. The hot water was on, and so I turned this off to find that the upstairs radiators warmed quickly, but the downstairs ones remained totally cold. Then, turning off the upstairs zone and turning on the downstairs zone only caused instant heat in the downstairs radiators. Adding the upstairs zone and the hot water left everything fine.

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    Default Re: Plumber can't fix two zone system - problem downstairs

    I can't stop thinking that this must be some problem with electrics. You clearly said that you can actually make all the zones work at the same time so it doesn't look like problem with plumbing to me. You should check the position of motorised valves to find out whether they are opened when you think they should be. You can try touching the pipe right before and after valve. Also you didn't mention what sort of valve you use for heating water? Is it mid-position or splitter valve? Did your problem started on its own or have you been doing some changes?

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    Default Re: Plumber can't fix two zone system - problem downstairs

    Many thanks. The problem started before Christmas when I had one cold radiator at the end of the circuit downstairs. I got the plumber in and he changed the pump and the motorised valve to the downstairs zone. He then discovered a lot of limescale build up in the splitter going to the vent (I don't know what to call things, I am afraid). He cleared this. The problem that I have described has existed since then, although he has been back once and drained the system - he had left a chemical cleaner in since his first visit.
    The motorised valves seem to work exactly as they should, as do the thermostats, and so I don't think that it is a problem with the electrics. Could the limescale blockage have caused both pumps to fail?

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    Moderator toscal's Avatar
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    Default Re: Plumber can't fix two zone system - problem downstairs

    I'm inclined to agree with kundrik in that it might be either an electric problem or the valve hasn't been fitted correctly. Quite often the motorised valve appears to be working, because in certain conditions it works but then add another condition to the equation and it stops. Do you know what type of valve you have. Is it a three way (there are two types one commonly refered to as a y valve. This has an input and then directs flow to either one of the outputs, but not both. The other type can direct flow to either output or both. Or is it just an simple on off valve. He may have fitted the wrong type of vavle or fitted the right type but the wrong way round. Which would explain why it works in a certain order.
    It might be an idea if you can to try and trave the system and draw a plumbing equivalent of a circuit diagram. I always think of plumbing in terms of electronics, pipes as wires, non return valves as diodes etc. Then for me its easier to understand as I'm not a plumber.

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    Default Re: Plumber can't fix two zone system - problem downstairs

    The valves are simple on/off ones: Honeywell V4943H Motorised Zone Valve.
    The feed from the pump goes three way with a motorised valve on each, one for the hot water, one for the upstairs zone, one for the downstairs zone.

    I thought that I would try something else today. When I went out this morning I left the timer on for the downstairs zone, but off for the upstairs one. I expected that at least it would be warm downstairs when I got it. It fact, the first two radiators downstairs were hot, but not the rest.
    I then went through by ususal procedure: turn it all off, turn on the downstairs zone then turn on the upstairs one. Lo and behold, all radiators warmed up almost instantly.

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    Automated Home Jr Member nickgale's Avatar
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    Default Re: Plumber can't fix two zone system - problem downstairs

    My suggestion is eliminate the electrics first - the 'flow' is as follows:

    Prorammer / timer turns on zone, i.e. the O/P terminal of timer for that zone becomes live, this is fed to the room 'stat which in turn feeds the motor of the valve for that zone. So if the timer is on, the 'stat is calling for heat (turn it as high as it goes) then the live feed to the valve motor should be live (usually the brown wire in the valve cable - neutral is blue) Check this is happening first.

    If all is OK then when the valve is open (i.e. motor is running) then a microswitch on the valve should close which turns on the boiler and pump - these are sometimes orange and grey cores from the valve cable. One side of the switch is connected to live, the other to the boiler input. Check that the microswitch is closing correctly every time the valve opens and when it does close that the boiler is firing up.

    If all is well on the electrics then it's time to call back the plumber. However I suspect this could be a wiring issue, I've met many colour blind plumbers who've changed pump heads before!

    Hope this helps?

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    Default Re: Plumber can't fix two zone system - problem downstairs

    The electrics would appear to be fine. The pump is now making a different noise and the end radiator is not hot. I have contacted the plumber who says that he confident that there is a blockage in the heat exchanger in the boiler and that he will quote for a new boiler and will flush the system when it is fitted. He also said that I am welcome to get a second opinion. Do I pay his bills which now amount to 435? Do I get another plumber? Your advice would be appreciated.

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    Default Re: Plumber can't fix two zone system - problem downstairs

    Sounds rubbish to me. If there was any blockage in the heat exchanger then radiators wouldn't warm up at all, would they. It's next to impossible to offer any advice without the electrics diagram and plumbing diagram. You should probably seek second opinion from someone as far from your place as possible. Just to make sure it's not one of plummer's mates.

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