Posted 20 hours ago

Honeywell ST699

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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. 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?). 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). 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!).

Also on your prior ST699 connections. The hard link from L to 5 means that when the hot water was "off" power would have gone across to 3 (CH-On) 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. 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. 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.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... Is it as simple as looking at a wiring diagram for the ST699 and attaching to the corresponding connection of a new timer?

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. 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 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. 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? 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!When it didn't work, I've Googled again and come across this Forum. Whilst I can find a few issues other users have had, I can't find anything that relates to my issue. I have noticed however, that the old wiring to the ST699 that is redundant, wasn't as per the diagram I saw in one of the posts. I have cables linking: 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... I've been doing a lot of research on heating systems recently, and for those that have seen my other topic I've been having trouble with a cold radiator which I think will need new valves.

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