I would suspect one of the switches is sticking and causing the intermittent fault you describe that makes the boiler stay on occasionally.

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.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. If you need any assistance with that, post back details of the existing room thermostat and a photo of its wiring connections. Hi Leesparkykent, thanks so much for your reply, still unsure about the current connection from boiler to pin 8 on old st699, so have a wire to go somewhere still on the st9400c? If there is an existing room thermostat somewhere, that should either be left in situ and set to its maximum setting so that it doesn't interfere with the operation of the Hive, or decommissioned by removing it and making a small modification to the wiring to bridge the switching circuit.

Again, it's down to the layout of the various heating components in your home and the personal preferences of the original installer. To fix downstairs would probably require proper room sensors and better radiators for the size of the space it is heating, and new windows and doors wouldn't hurt either! And when the Nest Protect senses smoke, it can turn on Nest Cam to help find out where it came from.I assume the current picture of the ST699 is after it has been removed from the wall and it's sitting on a table so to speak. For example, one answer shown below mentions the link from 5 to 8 being removed which I dont have, I have a direct link to 8 from the boiler, so not sure where to wire this to on the st9400c. As I say, I looked at the replacement wiring diagram and it all looked straight forward, so I removed the cables and put them into the terminals indicated. All other connections are clear on the diagrams supplied by Honeywell apart from this wire from the boiler to terminal 8. Every damn time I've shut off the power to do something, I'm forever having to stand there with my fingers pressing the buttons to reset the idiot thing.

With the older type of systems, (without motorised valves) it's not possible to have the heating 'on' without the hot water being 'on' as well. 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?If your existing programmer also controls the hot water, then make sure that the new one has the same facility. Due to planned maintenance, there will be a slight change to our usual dispatch deadline on Friday 3 rd November. 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! 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. For a gravity HW system, the hot water coming on fires up the boiler and the central heating being on powers the pump.

Due to the size of the rooms I'm not sure TRV's would help as it would be cutting off before the whole space was to temperature.The guides I have seen describe removing the link wire between 8 and 5 for the basic configuration which is different than mine. Setting times for central heating and hot water to switch on and off can help reduce your home's energy consumption.