3 point actuator issue (Drayton MA1) - confusing fault

elsmandino

Hi there.

My central heating system (separate water tank) has developed a fault and I cannot quite worked out was has happened.

A few days ago, I noted that the thermostat was telling the central heating to come on but nothing was happening.

The acutator was in the default hot water position (W) - if it were working, the acutator would have either been in the middle (M) or central heating position (H).

I did some testing, however, and if I used the lever to manually move the acutator to the M position, the heating works fine.  Furthermore, if I turn off the hot water but keep the heating on, the acutator moves to H position automatically.

Just to confirm - when the acutator is in all three positions, the boiler fires up as expected (assuming the central heating and water tank thermostats are calling for it).

The fault seems to be with getting the actuator moving from the first position automatically.

Although the motor seems to be working (as the actuator moves from M to W on its own), I tried swapping the motor for a replacement but have the same issue.

Any advice on what to do would be much appreciated - do I need a whole new actuator head?

Section62

elsmandino said:

Although the motor seems to be working (as the actuator moves from M to W on its own), I tried swapping the motor for a replacement but have the same issue.

Any advice on what to do would be much appreciated - do I need a whole new actuator head?

Have you checked the markings on the valve body (often A and B, but could be HW and CH) match the pipework - i.e. that the "HW" port goes to the hot water cylinder and not the central heating?

These valves usually work by the motor moving the valve 'ball' to the mid-position and/or then to block the unwanted port.

The 'return' is usually by spring loading, not positive drive from the motor.  Hence just because the actuator moves, doesn't necessarily mean the motor (and control circuits) is working as it should.

elsmandino

Section62 said:

elsmandino said:

Although the motor seems to be working (as the actuator moves from M to W on its own), I tried swapping the motor for a replacement but have the same issue.

Any advice on what to do would be much appreciated - do I need a whole new actuator head?

Have you checked the markings on the valve body (often A and B, but could be HW and CH) match the pipework - i.e. that the "HW" port goes to the hot water cylinder and not the central heating?

These valves usually work by the motor moving the valve 'ball' to the mid-position and/or then to block the unwanted port.

The 'return' is usually by spring loading, not positive drive from the motor.  Hence just because the actuator moves, doesn't necessarily mean the motor (and control circuits) is working as it should.

Hi there - yep all matches up correctly to the pipework.  The current actuator was installed years ago and has been faultless until now.  Just suddenly stopped working - no changes to timers or anything like that.

I just assumed that the motor was broken but as the acuator can move from M to H on its own, it seems that the motor is working.

I am wondering whether there is perhaps a PCB fault (on the actuator) that is preventing the heating thermostat from telling the actuator to move the motor from default W position.

grumbler

I'd check the voltage on all wires/terminals of the motorised valve:

https://flameport.com/electric/central_heating/heating_wiring_Y_plan.cs4

RonRamsgate

Fault Could be in the brass valve body where the moving part {immersed in water} has got tired, a little seized up, or physically sticking on the past port of demand.
Thats assuming the system is wired up correctly with the programmer and cylinder thermostat giving correct voltage demand  to move the valve body.
As Grumbler has mentioned, checking the voltages on all of the motorised valve wires is super important. Every system is Bespoke Some systems are wired up to give central heating and hot water simultaneous ~when hot water demand ceases so will central heating but central heating will commence when the cylinder stat again calls for heat.
Sometimes that is the way it has been designed of left following other component exchanges

Maybe purchase the brass valve body, attach it to your actuator and switch your programmer,cylinder stat, room thermostat in different combinations of demand and watch the valve motor/close in different demands.

Since the introduction of wireless/internet heatig/water controls its even more bespoke. More room for error 

ThisIsWeird

You've replaced the motor, but not the whole head? It's worth at least remove the head so you can check the brass valve below - it's usually only two screws.

The spindle on the valve should be smooth and easy to move through a ~30-ish arc? It should thunk solidly at each end of travel as the ball valve makes contact.