Honeywell ST699

Product Information

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?). 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... The boiler seems to be working fine. I did have to re-ignite the pilot light as it had gone out prior to me discovering my problem. 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.

This has lead me to think that while I'm replacing valves anyway I may as well use the opportunity to fit Thermostatic valves to all the upstairs radiators. I always thought I would need to replace the boiler system to get these but (unless I'm very mistaken) it's just a case of swapping the valves on the existing system. Not so worried about downstairs but our upstairs rooms are very prone to overheating and I think TRVs would really help and save money.

Why Use The Engineer Scheme?

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. 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. I have used only the hot water (HW) on twice a day timer over the summer. But not used the central heating (CH). I have recently changed to using the CH & HW and set the timer for HW & CH on twice a day. 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.

Is it a DIY job or something a professional should do, baring in mind I don't want to replace the whole system, just the timer/thermostat of the existing system? 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. Is it as simple as looking at a wiring diagram for the ST699 and attaching to the corresponding connection of a new timer?Over the summer and up to this point I have been getting the HW as expected, so the timer was doing its job ok. I do know that there is a Grundfos pump in the airing cupboard next to the cylinder and two white boxes connected to the pipes which I believe are motorised valves, but that is the extent of my knowledge - the airing cupboard is a bit of a spaghetti junction or pipes and wheel valves, and I don't really know what any of them do! I just opened them all when I first moved in and hoped for the best, I've never touched them since lol. 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? I don't want to spend too much time figuring out the problem if the easy solution is replacing the timer and job done.