Yep like that - they're called 'Lifestyle 2-port motorised valve', there is one underneath the pump on a pipe that doesn't go into the cylinder, and one on a pipe that come off the other pipe and goes into the cylinder about halfway up it. They've both got what looks like a switch with A - B settings, the one on the pipe running down past the cylinder is set to B, and the one on the pipe running into the cylinder is set to A, someone has also written on this one with a marker pen putting a C next to the A and an O next to the B (presumably meaning open and closed?). Does that mean hot water tank in airing cupboard which is heated via the boiler? (You may also have a separate immersion switch for the tank). But this has got me thinking, why stop there? Our boiler is controlled by an ancient looking Honeywell timer which from Googling I think is a Honeywell ST699 (except our version features a delightful brown/beige colour scheme!) There is also an equally old looking thermostat dial in the hall (just above the radiator which doesn't strike me as an ideal location!).

You had a hard wired link between Live, 5 (common for CH) and 6 (Hot water on). That's why I thought your hot water was permanently on. There was also a hard link between 3 (CH on) and 7 (HW off). Then there were connections to all four terminals for CH on/off and HW on/off which is not normal. So I wonder if the other end of those wires go to the expected places. As an aside my 'bay' window is more like a box on the side of the house, it's not full height and as far as I can see the large window sill is the only thing separating it from the outside, which seems like a horrible design from an energy saving/warmth point of view considering all the other walls have cavity wall insulation.Whilst wire colours do necessarily mean anything on a central heating system, the combinations you have are a bit unusual. For example blue being used for CH on & HW on and brown for hot water off. That's based on your indication above about wiring on ST699. I would really like to get rid of the thermostat in the hall altogether for cosmetic purposes and I would love to have more flexible control over the heating than the draconian timer we have now that has one setting for all days for both the heating and the hot water at the same time. Ideally I would like a modern digital timer with flexibility for multiple programmes for different days and times and a wireless thermostat in the living room to control the temperature. And one that doesn't lose all it's settings whenever there is a power interruption! My question is how difficult would it be to replace just the timer and thermostat (with a wireless one) without touching anything else in the system? Would I need to replace it with a Honeywell model or are all the wires like for like? Is it as simple as looking at a wiring diagram for the ST699 and attaching to the corresponding connection of a new timer?

The only reason I wasn't going to bother with downstairs was because we don't really have trouble with the heat levels downstairs, if anything it's hard to keep it warm even when heaters are on constantly as it is a large open plan space and has a very large bay window at one end and French doors at the other.If you have a S-Plan system with a single heating zone 3 for HW-On and 4 for CH-On, nothing to either 1 or 2. You can have hot water only, but you can't have heating only - the hot water has to be on for the heating to work, although I have no idea how the two are connected from a system point of view... Prior to the ST699 failing did everything work as you would expect. What you programmed as the hot water on/off cycles is what happened. Likewise for the central heating. Sounds like there would be a bit more work involved in sorting the flexibility side out, as well as updating thermostatic room control, so I think I might just leave that bit alone until the day comes that I install a whole new combi-system. very pleased with service and correspondence I received from you ,I will have no hesitation to use you again

Having said that I suppose it can't hurt to put a TRV on the kitchen radiator as that doesn't really need to be on while we're in there cooking, worth considering I suppose... Can you please provide a picture of the ST9400 wiring. Do you also have any pictures of the prior ST699 wiring to compare. If you don't have a picture of the ST699 wiring can you carefully outline the connections on the ST699 (terminal, wire colour, etc) and to which terminals they were moved for the ST9400. You said "I have cables linking:" did you mean "I HAD cables linking.. on the ST699". It's all connected and I've set the time and date, all is okay. However, even though the lights come on, it won't fire up either the heating or the water!Unfortunately wiring colours tend to be meaningless with heating systems. One installer may use a blue wire for a certain purpose another may use a brown for the same function. So never assume a blue wire is actually being used as a neutral it may be being used as a live. It's what a wire is connected to at each end that determines its function, not the colour of its insulation. That said based on your prior ST699 wiring. I think your hot water was permantly on as you had linked L->5->6 . And the HW-OFF (7) was linked to CH-ON (3).