No heating - MA1 actuator not moving - valve not seized - HW fine but interrupted if UP2 HW switched on

[ht96]

I have the following setup:

• Glow-worm 30R regular boiler
• Hot water cylinder with cylinder thermostat
• British Gas UP2 programmer (Invensys)
• Honeywell T6360B1028 mechanical room thermostat
• Drayton MA1 3-port motorised valve

The problem:

System was fine before summer. No work was done. Now, central heating isn’t working. With heating ON at the UP2 and the room thermostat turned up to 30°C, the MA1 actuator remains at W (hot water position). No movement, motor noise, pump activity or boiler ignition

Hot water works, but behaves strangely:

• If heating is already ON at the UP2, the boiler won’t initially ignite for HW if it is switched from off to on, even with the cylinder thermostat calling.
• Switching heating OFF allows the boiler to ignite and heat the cylinder for HW on.
• Once the boiler has ignited for hot water, I can toggle heating ON/OFF without interrupting it.

What I’ve checked:

1. Replaced the MA1 actuator head with a second-hand unit — identical symptoms.
2. Tested both actuator heads detached from the brass valve body but electrically connected — neither moves, ruling out a seized valve spindle as the cause of no movement.
3. Honeywell room thermostat clicks normally.
4. Continuity between thermostat terminals 1 and 3 is present only when the thermostat is turned up (tested with wiring still connected).
5. UP2 heating and hot water indicator lights operate normally.
6. Confirmed UP2 terminal 4 (CH ON) has a red wire connected.
7. System worked perfectly last winter. No wiring or controls have been changed over summer.

Current suspicion:
Possibly a failed UP2 heating output, a wiring/connection fault, or missing heating demand reaching the MA1 white wire.
I have a multimeter but haven’t yet measured the live control outputs. And it's only CAT2 up to 300V, apparently I need a CAT 3?
Questions:
Does this sound like a faulty UP2 programmer or something else in the Y-plan control circuit? Could the unusual hot water behaviour be related to the missing heating demand?
Any advice on narrowing down the fault would be appreciated before I start replacing more parts or just call an electrician/plumber.

 

[Collectors]

I might be wrong, but how old is the system as it sounds lke the older way of doing things where the hot water always had priority & would then switch to heating when the hot water stat was satisfied. It sounds like the stat hasnt switched over to say lets heat the rads.

 

[ht96]

You wouldn't believe it.

A knock on the top right of the UP2 has triggered the heating. took 3 knocks, the first 2 briefly demanded heating (temp on boiler flashes) and rescinded it, the third was permanent.

If the UP2 needs replacement, could get a replacement front unit for the UP2 or switch over to one of the smart ones.

Is it simply plug and play with the same wiring as UP2 in NL1234 usually if I go for something like the one attached?

 

[Collectors]

Its either the conection point or the relay inside has fered up. A lot of those back wiring plates are standered & on many you can use differant makes without unwiring everything.

 

[CountryFan]

Could be the relay output. What I find strange is, an MA1 3 port, but no hot water off connection.

 

[fixitflav]

Drayton MA1 3-port motorised valve

Is it mid-position type or either/or?