Drayton MA1 3 port valve

[Tezbedz]

Hi we have just had a problem with the central heating coming on whenever hot water was on.
Have checked the 3 Port Valve; Drayton MA1 which was jammed solid. I have removed the actuator (click fit) and replaced the valve, the original was corroded solid. ( have also checked pump and removed scale/corrosion)
Replacing the actuator and filling the system, we seem to have the same problem.
Could the jammed valve affected the actuator?
Is there a way of testing it? Have tried switching on HW on its own and nothing happens to valve, switch off and switch on CH nothing happens to valve but, pump starts running and boiler flashes. I am filling a hot bath to see if valve opens to HW when pump & boiler comes on. If not would I be right in thinking actuator is duff and a replacement needed

 

[buck51]

IIRC they have two springs in the actuator the posts they are anchord to snap off, I moded mine by hooking the springs to the base plate, where the pegs had snapped from.

 

[D_Hailsham]

Hi we have just had a problem with the central heating coming on whenever hot water was on.

I had a very similar problem on Saturday evening.

The wife had turned the heating up (British Summer ) during the evening; it should have gone off at 2300hrs. Just after midnight as we were getting ready for bed, she calls up to me saying that the radiators were boiling hot - hotter than they ever got in the winter.

I checked and the boiler was definitely working. I then checked the wireless programmable stat which showed the system should be off and the relay box was not showing a light. The hot water was still on (goes off at 0030hrs), so I turned the cylinder stat to minimum but the boiler continued to run. So I turned everything off saying I would check it out on Sunday morning.

To cut a diagnostic story short, the problem turned out to be the ACL Drayton HTS3 cylinder stat was sticking so the contacts remained closed even when the water was up to temperature. The sequence of events meant that the mid-position valve was held in the CH only position, so only the rads got hotter and hotter.

Sunday morning/afternoon was spent trying to locate a Honeywell cylinder stat; I eventually got one at Screwfix 15 minutes before they closed.