Tado for S-plan system with an immersion heater

[stem]

I noticed the Bianco zv22 motorised valves obviously click when the thermostat clicks and I think I can hear the valve turning but I noticed the valve is quite old and that the lever on the back moves slightly but is quite loose when I wiggle it..

That's as it should be. When the valve is closed, there should be resistance when the lever is moved from auto to manual. When the valve is open the lever is loose and floppy when moved.

Inside the motorised valves are microswitches that operate the boiler when the valve is open. So, maybe when the CH was on yesterday its microswitch operated the boiler, and so if both CH and HW valves were open, both would get hot water from the boiler.

If today you just have HW on, and the switch inside its motorised valve is faulty then the boiler won't start. Odd though it's happened at the same time as the programmer has been changed. If the switch is faulty putting the old programmer back won't solve the problem.

The wiring in the photo looks to go where I would expect it to. Or, at least the wires are in the terminals I would expect them to be in. The HW NO wire appears to have insulation trapped under the screw, which it shouldn't have (as a comparison, the wire under the L terminal is spot on) and the outer white sheath of the cable should be securely fixed under the cable clamp provided so that there is no strain on the electrical connections. and none of the coloured conductors are visible below it.

 

[ericmark]

In the motorised valves I use, the cam pushes the micro switch on, and the spring in the valve turns it off, they can stick, but this normally means the boiler and pump continues to run and the by-pass valve opens. If plumbed correct.

So better looking at the sequence of events, and where does it stop.

1) The programmer turns on.
2) If not built into the programmer, the thermostat or hub turns on.
3) The motorised valves opens.
4) The micro switch turns the boiler and pump on.
5) The radiators get hot.
6) The TRV's close.
7) The by-pass valve opens.
8) The boiler senses the return hot water and start to modulate.
9) The boiler can't modulate any more, so it starts a mark/space ratio.
10) The anti-cycle software kicks in and the boiler off time gets very long.

What you can have is the boiler skips some stages, so if the motorised valve fails to open, it jumps to 7.