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Thread: Trouble with 3-port Valve

  1. #1
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    Default Trouble with 3-port Valve

    Hi, this is my first post/cry for help.

    Since moving into this house about 4 years ago (house is 8 year old), the central heating has never been quite right, in that the central heating would come on whenever the hot water is on, but we lived with it by turning down the TRV's in summer.

    Recently, the boiler has been refusing to ignite when the programmer/cylinder stat has been calling for heat. I played around with the 3-port valve (Sunvic SD2701F) and got it working for a short while by flicking the manual/flush lever. But it stopped working again after a few days. I tested the valve actuator by altering the room stat and cylinder stat and found that it was duff, so I bought a new one. Once fitted, the boiler fired up first time, but I still got central heating whether I wanted it or not. Then after a few days, the boiler would not ignite again.

    I took off the actuator and turned the valve spindle by hand. By luck more than anything else, I heard the boiler ignite and hot water began to flow. To my surprise, it went throught the divertor and off to the hot water cylinder only. No CH! I think that's the first time I recall it EVER doing that. So, with the cylinder stat turned up and CH turned off, I try and fit the actuator to the valve, but it wants to be on at 90 degrees to where the fixing plate is!

    Could this explain why the system has never worked properly, and what can I do to fix it (bar draining the system and checking the valve/fitting a new one).

    Thanks.

    Sean

  2. #2
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    Default Re: Trouble with 3-port Valve

    Have you replaced the 3 port valve? Sounds like to me that is the problem. You can replace just the head, so no need to drain down. What boiler do you have and is it a sealed system?

  3. #3
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    Default Re: Trouble with 3-port Valve

    I fitted a new actuator to the valve a few days ago as the existing one was definately bust (not moving to commands from stats) but it didn't cure the problem, so yesterday I part drained the system with a view to changing the valve body itself. However, as the existing one looked fine, I made sure it was lined up properly with regards port A, B, AB and put everything back together. It then worked first time, and has continued to do so over the weekend. I'm keeping a close eye on things over the next few days. The downstairs rads are taking longer to warm up than they did before I drained the system, but they get there eventually. Air? Pump? (I'm sure the pump is running).

  4. #4
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    Default Re: Trouble with 3-port Valve

    If the downstairs are taking longer to warm up, assuming that there is no air left in the rads after you have drained them, the best thing to try first is shut all the upstairs rads off, then all the downstairs bar one. Run the heating just on that rad then open the others in turn, downstairs first.
    BEFORE you do all that, manually open the 3 port (heating off) and bleed all the rads again. sometimes air can get trapped there. Also check for finger vents around the cylinder and valves. It wont be the pump.
    If you havent already done so, be sure to put some inhibitor treatment back in the system. That helps keep it clean and running well.

  5. #5
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    Default Re: Trouble with 3-port Valve

    Thanks. I will try that tonight.

    I did not drain the entire system. I used the drain point on the return at high level above the boiler on the ground floor (Ideal Minimiser FF50). I assume this will not have drained the ground floor rads. I noticed that the drain-off was exceptionally clear, as clear as tap water. This surprised me, I was expecting the water to be dirty!

    I have bought some inhibitor but I didn't put any in this time around. I wanted to make sure it worked first, in case I had to drain it down again. Should I drain the entire system prior to installing fresh inhibitor, to give it a bit of a clean?

    Thanks again.

  6. #6
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    Default Re: Trouble with 3-port Valve

    Na, I wouldnt bother to drain it all down if it come out nice and clear. Must have been well treated in the past. I would definatly add at least half of a new bottle though. Probably be worth sticking the whole lot in. Cant do it no harm!
    Good luck

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