central heating 3 way valve problem?

I have had my cental heating for aprox 7 years, during which time the 3 way valve has been replaced twice, it now seems to have gone again, I think that the guy that installed and services it has not put any inhibiter in, the problem is that the radiators come on only when the hot water comes on,[which is what happened the last time] would putting inhibiter in now, going to free it up, [if that is the problem] or is there anything that would free it, or will the whole or part of the valve need replacing, and then inhibiter added? I would appreciate any help as this has cost alot of money

Reply to
Richard
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Oh dear. Not putting in inhibitor is a very false economy as you have discovered. Really, the fitter doing the work should do it and it should be checked as part of the annual service. It's sloppy not to do this, although cynics would say that it's a way of generating call-out business in between.

At any rate.... adding inhibitor now is quite unlikely to free up the valve.

If you are lucky, it is only the body that will have stuck. You can take off the motorised head by undoing a couple of screws normally and then there will usually be a projecting tab from the base of the valve. You can try turning this gently with pliers to see if you can free it.

At the same time, you can check that the motor is running in the head OK by operating the thermostats and seeing if the cam in the base of the head turns.

It's reasonably easy to replace the motorised head if you need to - they are not expensive - you just need to take care over which coloured wire is which.

Assuming that you can fix this, then it would be a good idea to thoroughly flush the system and then add some flushing agent. Run the system according to the instructions - this normally means normal use hot for a week. Then flush thoroughly again and finally add inhibitor.

Reply to
Andy Hall

Obviously you ought to have inhibitor in your system, but the lack of it is not necessarily the cause of your immediate problem.

The mechanical part of the valve can get stiff to turn regardless of whether there's any inhibitor in the system. And the electrical part (actuator) can fail at any time - and often does!

I suspect that your problem in this instance is caused by a problem - maybe a failed micro-switch - in the actuator. When there is a HW demand, the boiler and pump are controlled directly by the feed from the programmer via the cylinder stat. Once the HW demand is satisfied, the boiler is controlled by the actuator - using a micro-switch which operates when the valve gets beyond the mid position. There are several possible modes of failure:

  • duff motor in actuator, so that valve stays at HW position
  • very stiff mechanical valve - such that actuator isn't powerful enough to move it far enough
  • valve *does* move but micro-switch fails to operate

You'll have to do a bit of detective work to find out which it is!

Reply to
Roger Mills

Thankyou very much for your help and advice, I followed your instructions and was able to turn and release it carefully with pliers, and it seems to have done the trick, by the way it was stuck in the middle possition, [the diagram has fallen off so not sure what that is]. I am going to leave it a day or two to make sure it is working properly, then flush and add inhibiter. Wish I had known b4 about no inhibiter, certainly causes problems. Thanks once again I am extremely grateful, regards Richard.

Reply to
Richard

For future reference, this sticking commonly happens at the start of the heating season when the valve has been sitting in one position for HW the whole summer. It can still happen with inhibitor.

Some thermostats and boilers have a valve exercise feature which simply operates the valve every so often.

Otherwise, it makes sense to fire up the CH briefly every couple of weeks during the summer.

Reply to
Andy Hall

Thanks very much for your reply, I think have found that it was one of the things you mentioned, the mechanical valve? as I tried the motor, suspected the microswitches, but thankfully was able to free it up, I will of course put inhibiter in soon, and looking at the other posts on here replace at the most every 4 years thanks once again for your help, Richard.

Reply to
Richard

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