Central Heating - Constantly on?

[terry_gigg]

Hi, can anyone help me identify why my CH is constantly on? Following the recent cold snap I set my Honeywell controller to switch the heating on the following morning. All was well in the morning, however when the hot water only was due to come on in the evening, the heating came on aswell, even though the heating controller was set to off and the thermostat was turned to its lowest setting (off!) I'm beginning to boil, walking around in my underware and the kids are sharpening the harpoon!!

[Set Square]

Have you got a Y-Plan system [See

] with a 3-port mid-position valve to control the water flow to the CH, HW or both?

If so, sounds like the valve is sticking. The motor will have moved it to the mid or CH position when you had the heating on. A spring is supposed to move it back to the HW-only position when the CH demand is removed. If the valve is stiff - particularly after not being used during the summer - the return spring may not be strong enough to overcome the stiction.

If you think this may be the problem, remove the actuator from the valve (couple of screws). If the actuator then rotates when it's no longer attached to the valve, that is fairly conclusive. Try to move the valve by hand. The shaft should rotate through 45 degrees either side of the mid position - either using just finger and thumb, or with *light* pressure from a pair of pliers. If it needs a lot of force, it is too stiff. You may be able to free it by turning it to and fro. Otherwise, it will have to be replaced.

[Harry Bloomfield]

terry [e-mail] formulated on Wednesday :

It sounds like your 3 port valve has stuck. Turn the system of and undo the two screws which hold the actuator (the motorised bit), onto the valve. Check the water valve is free to turn with just a little more than finger pressure. Make sure the actuator returns to it default position when not powered up.

[Malcolm]

We had a similar thing, have the heating switched off and hot water on, then when the timer kicks in all the rads got hot, and the room stat had no effect. Not knowing if it was the roomstat, the controller or the three position valve I purchased a complete kit from Screwfix for less than £60 (enter quote number 94777 in the box on the screwfix website)

Now the system is working fine and hopefully our gas bills will be a lot lower this winter

Malcolm

terry [e-mail] wrote:

[terry_gigg]

Thanx for the help Set Square, as you can see by the time I have been hard at it, sadly the Valve was so corroded i had to drain the whole system down and replace it! you were spot on with the diagnosis :)