3 way valves


Postby Ray Lifton » Mon Oct 06, 2008 7:50 pm

My heating circulation to the radiators is poor. I know I have 8mm microbore feeds which is not great on a 20 year old property, but I'm sure I have a problem with my 3 way valve as since the heating has been back on my hot water is much hotter.
Is it possible that the 3 way valve is short cuircuiting through the cylinder and can you get a repair kit or is it easier to replace the valve fully?
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Postby plumbbob » Mon Oct 06, 2008 11:20 pm

Not sure why you are pointing a finger at the three way valve as it seems to be operating ok. ie, you are getting hot water, central heating, and are not complaining the c/h is on when only the hot water is supposed to be on.

Cold radiators are caused by lack of flow.

1. The system is sludged up.
2. The bypass valve is open too far.
3. The cylinder lockshield is open too far.
4. The pump speed is set too low.
5. The system is not balanced properly.

The hot water is probably hotter because the boiler is firing up for longer since you have had the heating on.
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Postby Ray Lifton » Wed Oct 08, 2008 6:42 pm

I have washed through the system last year due to simalar problems and spent some time trying to balance the system so that all rad's got heat.
My suggestion is that is it possible that the three port valve is not fully closing when the hot water is to temperature and allowing the boiler discharge to short circuit through the tank, returning to the boiler and shutting the boiler down on it thermostatic control. This would also answer the question why the hot water is so much hotter than the tank setting.
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Postby plumbbob » Thu Oct 09, 2008 12:46 am

Ah, yes, I see your point about how the hot water in the cylinder could get hotter than the cylinder stat setting. Of course, it could be due to the boiler firing longer. Test it by manually reducing the cylinder stat until it clicks off then fire the boiler up with the heating on and see if the pipework to the coil heats up. Obviously, it should remain cold.

The point against this though is the system should be able to be fully hot with the radiators AND the cylinder coil being heated simultaneously. If the lockshield valve in the cylinder circuit is missing or fully open this would indeed cause poor flow in the heating circuit.

Check for a bypass valve and ensure it is just cracked open as the cylinder lockshield should be.

If any of the radiators get red hot, shut the lockshield valve fully down then just open until you hear the flow of water start.

The trouble with 8mm is it needs such a high pressure in the system to force the water round and if a short circuit is possible then the water will gladly take it.

If the valve is leaking, then it needs to be replaced. Some spares are available, but only for the electrics and gearing. Not the ball valve assembly.
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Postby Ray Lifton » Sat Oct 11, 2008 5:57 pm

Thanks for your pointers and help.
I'm not sure I seen a lockshield on the cylinder, so I'll have another look.
Regards
Ray
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