Honeywell ST699

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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? The boiler is due its annual service and a good clean as we live in a flat with a dog and fluff. But I don't think the problem is related to the boiler. 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. 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.

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.

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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.

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... Whilst Hive has an earth terminal it isn't actually connected to anything. Hive doesn't need an earth connection itself. The terminal is just there to 'park' any earth wires that happen to be present and keep them together so that they are safely out of the way of the other terminals.

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Over the summer and up to this point I have been getting the HW as expected, so the timer was doing its job ok. 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? 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.