Old system needs new controls

[Derek Peters]

I am trying to improve my father's old central heating system by fitting a programmable thermostat. Before starting the project I did some research and found advice that it is a straightforward process to connect the stat across the 'boiler on' feed from the controller, set the heating to continuous and let the new stat run the system. Unfortunately doing this means the DHW only function is disabled, there is no immersion heater, so no heating in warm weather means no hot water. If I connect the stat across the pump feed, the boiler is on 24/7 which defeats the whole point of the excercise. Installing an immersion is not an option so I am now stumped. Does anyone out there have any suggestions? Is there a wiring solution that I haven't thought of yet? I'm wondering if a cylinder stat might control the boiler, and then the room stat can control the CH valve and pump. Any advice most welcone please.

 

[Dan Robinson]

System details?

 

[Derek Peters]

Not sure about the boiler, I think a Baxi vintage early 1980s, back boiler with gas fire front. Controller is Sunvic 207XLS, boiler is on terminal 4, CH pump and valve on 3, nothing on 1 or 2. I want to fit a Salus RTF500.

 

[Agile]

Do you know if it is gravity hot water?

Or is there a three port motor valve?

Tony

 

[DP]

Derek can you run CH without hot water?

 

[Derek Peters]

Sorry, been out of reach for a long weekend. Yes, it's gravity hot water and no there is not a 3 port valve, just a single port that prevents convective/gravity feed to the radiators. No I cannot run CH without hot water, in fact since there are no 28mm connections on the cylinder that might indicate a calorifier I think it might be a direct system.

 

[DP]

By single port you mean a two port valve I take it
No 28mm. Is the cylinder flow and return 22mm, 15mm even, does the pump run when you heat water?

This post might help you achieve what you desire
//www.diynot.com/diy/threads/nest-thermostat.463626/