I have an old central heating system that I cannot afford to replace. I want to fit a programmable thermostat into the system to make it more efficient and I found some advice that said it is an easy job to wire it across the 'boiler on' feed from the controller, set the CH control to continuous and let the thermostat take over. I've found that with that set-up the DHW does not function, but if I connect the stat across the CH pump then the boiler is running 24/7 which defeats the whole object of the excersise. Does anyone have any suggestions as to how I can get past this. Is there a wiring solution, or is the only option to drain the system and install an immersion heater in the hot water cylinder?
we need to know what boiler you have and what control system you have in place, Poss some photos, boiler, airing cupboard ect, then should be fairly simple.
I think the boiler is a Baxi back boiler behind a gas fire in the lounge, vintage early 1980's but serviced every year and still going strong. The controller is a Sunvic 207XLS, the boiler is on terminal 4, CH pump and valve on 3, nothing on 1 or 2. I have bought a Salus RTF500 to put into the system. Sorry I can't do photos, it's my father's system I'm trying to make more efficient and he's over 100 miles away.
Bow, I don't think what you have is a 'system' boiler, but a conventional 'vented' type. I presume you have an expansion tank in your loft, alongside the cold storage tank? And I presume the pump in your system is a separate item, and not built in to your boiler? And I presume you have a 3-port diverter valve that looks a bit like this: http://www.screwfix.com/p/drayton-ma1-679-3-3-port-motorised-valve/81844 Can you confirm whether you do have these items, please? So, I'm also hoping that you have a separate 'wiring centre' - a box where all the cables go to? If so, we could do with a look at that too. Can you confirm - at the moment, your Sunvic 207XLS will give you completely separate hot water and central heating? Ie - if you turn on just the CH, it doesn't also heat up your hot cylinder?
To me it's a system boiler because it's not a combi, the cylinder is vented to the expansion tank. Thinking about the pipework on the cylinder it might be a direct one, there are no large diameter connections that would go to a colorifier. There is no wiring centre, just the Sunvic, which turns on the DHW when CH is called for. The valve is a single port, the heating is not divided into zones, it simply prevents convective heat to the radiators when DHW is on and heating off.
Hi Often when the back boilers were fitted, it was replacing a gravity hot water, pumped heating system. If you want to run the system with a programmable thermostat, the system will have to be changed, either a 5 wire three port, or two, single zone valves, to allow separate hot water and heating. If you have separate hot water/heating, then it's straight forward to add the programmable room stat. Just reroute the heating sw.live, from the timer to the common on the room stat and then the sw. Live from the room stat to the wiring centre ( leaving heating on constant) Simples! Regards Peter
You have a 'conventional' boiler. The only real difference is that a 'system' boiler is 'sealed' and doesn't have an expansion tank. And all the main components - pump, diverter valves etc) are all inside the boiler casing. Anyhoo, sounds as tho' you have a pretty basic gravity system for the DHW. I think. So, when you turn on the radiators, the hot water cylinder also heats up - you cannot stop it? I'm not familiar with 'gravity hot water' systems, so not sure how you'd wire up the Prog Stat. You were correct in the basic principle in your first post - you interrupt the wire from the timer for the CH, and insert the Prog Stat in there (also adding power for the PS unless it's battery), and then leave the CH timer 'ON' 24hrs, but that would apply to a fully controlled system - independent CH and DHW. You could change your system with the addition of a 3-port valve, but I wonder if it's worth it?
Thanks guys, I'm not going to set out on anything too complicated or expensive, it's not worth it given how little time Dad is likely to be living there given his age. I think I have two options, either fit a cylinder stat that will limit the boiler running time, provide constant DHW, and connect the PS across the pump and valve, or else drain the tank and fit a 2Kw immersion that I won't have to wire all the way back to the consumer unit.
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