But I see a post like yours, and I think of my central heating, I have two pumps, two motorised valves, the domestic hot water and bathroom radiator is thermo syphon, no control other than boiler run time as to domestic hot water, and closest plan is a C Plan, I still am not sure of pipe layout, but I have got a wiring diagram of the 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. So i will also need to move the programmer when i upgrade it, but im not sure what cable to use to extend the length. As this information is anonymised and aggregated it cannot be used to identify any individual user actions.

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... to the terminals of the dual channel Hive that have exactly the same functions. So N goes N, L to L, Hot water on, to Hot water on etc... 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.My question is, as we have had to move some appliances around the kitchen, the st699 is now awkwardly behind the fridge freezer.

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. 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. Yes N & L were previously in N & L on the ST699. Regarding the locations of the other cables, I'm pretty certain that I did the following swap, although, I'm second guessing myself now: 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. of the current 3 wires in the wall with the (neutral maybe?) with its box off but as shown in the photo previously all were just wired into seperate boxes. Any idea which to connect to get the circuit closed again?

However, the ST699 has two simple switches inside, one for heating and one for hot water, and so does the Hive. From an electrical point of view they are the same, so you are simply exchanging one switch for another identical one. For exchange purposes, what's on the other end of the wiring is irrelevant really, provided that the ST699 was installed and working correctly in the first place.

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! Ahh..............interesting. It was in the middle. I pushed it to the "manual" end a few times and allowed it to return to the middle. Then when I switched the main switch on, the pump ran for a second or two then stopped, which sounds to be what should happen.......................? As you have a 3-port motorised valve connected [the clue is that there is a wire connected to the HW off terminal] then inside the motorised valve is a microswitch that controls the boiler when the heating is required, which means the Hive won't be controlling the boiler directly. Hive controls the motorised valve, and when the valve is in the central heating position that fires the boiler. So hot water off on the programmer and hot water off on the tank thermostat but connect to the grey wire on motorised valve to turn DHW off, default is DHW on. Thanks Les. I have a multi meter and I'm reasonably competent at electrical stuff but I have little understanding of what signals what and when when it comes to central heating systems.

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. 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. I've attached pics of the ST9400C wiring before and after the swap (ST9400c Wiring 1) and a pic of the remaining wires in the ST699. 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?). 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.

Do you have a multi meter and able to trace the wires, in theory one core provides the live input to the boiler (#8) and one the live input to the pump (#3). I can see from your photo that there are two separate cables as the wires going ino terminals 1,2,3,4 on the ST9400 as they have slightly different characteristics Hi all I have a Y plan system with a mid position valve and original honeywell st699 controller. I replaced the wiring as shown. It seems that the hot water does not fire up the boiler on its own. It will work when heating is selected. I did not switch the system to gravity fed. If I change to this will it start working correctly. Hopefully someone can answer this for me. It's often the case that a standard cable L, N, E is used to connect a room thermostat and the N conductor is often used as the switched live. It should really have a brown sleeve over it (or red in the case of older installations) to indicate that it is being used as a live, but not all do, as you have discovered.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: