honey y system 3 way valve

[unclefewst]

have a problem with my mates heating system honeywell sundial y system with 3 way valve, room stat, cylinder stat and programmer,
circumstances are that both pump and motorised valve were changed some 2 years ago following a couple of new rad installations, system has worked fine, inhibitor in the water, however he has just returned from a week away on holiday, he has fired up his system calling for hot water only with the room stat down, the rad's are getting hot, obviously telling me the valve is not closing to the central heating loop, i cannot imagine the 3 way valve packing in so early, i have one in my house that has been there for some 15yrs, (but i regularly drain down flush and install bothe x100 and x200 for a nice quiet system, any suggestions would be appreciated and anything to try out first before costly outlay, regards Dave

 

[kevplumb]

valve might be sticking /stuck

can you hear it motor over when you alter the stats

 

[D_Hailsham]

fired up his system calling for hot water only with the room stat down, the rad's are getting hot, obviously telling me the valve is not closing to the central heating loop

If only hot water is being heated, the motorized valve is not in operation. It should be held with the HW port open by the spring in the valve. The boiler is turned on by the output from the cylinder thermostat.

Check that the valve has not been locked in the MAN position by the lever on the side; it should be in the auto position.

Are you getting the rads and HW hot or is it just the rads?

Read Mid-position valve working and Diagnostics

For starters, turn off the electricity to the complete system. This will remove any power to the valve, which will then go to the unenergised state - HW port open under spring.

Then turn on the HW side at the time switch only and check that the boiler starts/stops when the cylinder stat is turned up/down.
If this is OK, turn off the HW at the time switch and turn on the CH and do the same check for the CH using the wall thermostat.
If this is OK turn the HW on at timer and check that both thermostats are working properly. You need to check CH stat with HW turned up then with HW turned right down.