possible problem with honeywell 3 port valve?

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23 Aug 2011
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Berkshire
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United Kingdom
I have had a problem in the last few days with my central heating system. I keep my hot water and central heating on at all times, all year round and worked the heating with the room thermostat. That has worked well for 17 years. But, at the weekend my central heating radiators became so hot that they were impossible to touch and the house was like a sauna. I checked the room thermostat and it was still showing set at 15 degrees. I checked the room temperature using this thermostat and it clicked at 30 degrees. I turned the central heating off at the boiler (Potterton Prima F) panel control (Potterton EP2001). But, that made no difference. The radiators remained so hot that they could not be touched. So, I had to turn off the hot water at the control panel as well. I also turned off each of the radiators individually, except 2 which would not turn off due to the valves just going round and round. When I switched on just the hot water today, the 2 remaining radiators that I could not switch off turned back on and again became incredibly hot. But, there was no hot water available at the tap. It seemed that the radiators had used it all up. Just prior to this fault occurring one of the non-faulty radiators was leaking a lot of water from both its valves. I do not know if that is connected in any way to this fault. Can anyone help with a diagnosis. The 3 port valve on the tank is a Honeywell motorised valve.
 
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sounds like your 3 port is stuck in ch position.
but your cyl stat is calling for heat all the time due to the hw port being closed so heating the rads with no control from room stat.

check the lever on the end of the valve.
put hw on only heating off the lever should have resistance if you push it across or is it floppy ?
 
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So does that mean I need to replace the 3 port valve or the entire boiler?
 
So does that mean I need to replace the 3 port valve or the entire boiler?
The problem is in the control system, not the boiler.

Turn off the power to the heating system. (Setting the CH and HW timers to OFF is not sufficient.) This resets the 3-port valve to the HW open position.

Now move the lever across the slot from Auto to MAN. If you feel resistance and the lever returns to the Auto end when you release the lever, the valve is not sticking. The problem must be electrical.

If you want to have a go at diagnosing the cause of your problem, there are full instructions in How a mid-position valve works
 

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