Boiler has started acting up all of a sudden, strange behaviour.

[chazzer]

I live in 3 bed detatched house, the heating/boiler system is an old style one with a gas boiler downstairs and hot water tank upstairs with a 3-way zone valve actuator and LP522 2-channel digital programmer.

The system has worked fine since I moved in 7-8 years ago. Yesterday however noticed strange behaviour.

If I turn the heating on, the zone valve moves to H but the boiler doesn't start. If I then turn on the hot water the zone valve stays on H, the boiler starts and the radiators get warm until the temperature of the house reaches the thermostat temp then the zone valve moves to M.

If I only turn the hot water on, the zone valve moves to W, if I then turn on the heating the zone valve moves to M.

So currently the only way I can get my heating to work is to turn the heating on then turn the hot water on, selecting heating alone won't fire the boiler into action. As far as I can tell the zone valve is working fine, it moves from W to M to H as the options change. But with heating only selected it stays in H and no boiler action.

Any ideas?

 

[Deleted member 120897]

It sounds like it’s not making the microswitch inside and therefore not firing for heating. New actuator head or whole valve required (Depending on setup).

 

[Basher]

The two things that electrically switch the boiler on are:
1) a microswitch at the end of travel of the zone valve (combined with room thermostat etc)
2) the hot water cylinder thermostat.
Although your zone valve is moving, it could be that for some reason the motor doesn't manage to drive the mechanism far enough to operate the microswitch to turn the boiler on (or the microswitch has failed).
If you switch hot water on, and the cylinder stat is calling for heat, that will turn the boiler on, and the valve will stay in mid position to run both HW and rads.
The microswitch theory could be checked with a meter
Thats funny, Undertrained got there first!

 

[chazzer]

The microswitch theory could be checked with a meter

How would one go about going this?

 

[Basher]

How would one go about going this?

We are not supposed to give step by step instructions on these forums (for safety's sake), but if you are competent with electrics, the thing I would say is that (when disconnected) the orange wire from the 3 port valve should become live (ie 240V wrt neural) when the valve is fully over in the radiators position. Moving it with the lever, depending on the make of the valve, may not operate the switch, so it's necessary to have the valve powered for this test.
Obviously one would not be fiddling around in the wiring centre box locating the wire with the power on!

There are plenty of circuit diagrams on the web of how a Y-plan system is wired.
If you are not experienced with the above, the obvious solution would be to get some professional assistance.

 

[Loganliam]

The two components that electrically turn on the boiler are as follows:
1) a micro switch at the zone valve's end of travel (combined with room thermostat etc)
2) the thermostat for the hot water cylinder.

Despite the fact that your zone valve is in motion, it's possible that the motor fails to move the mechanism far enough to activate the micro switch and turn the boiler on (or the microswitch has failed).

The boiler will turn on if you turn on the hot water while the cylinder stat is signaling a need for heat, and the valve will remain in the middle position to operate both the HW and the radiators. Thanks