Chrono- Proportinal Thermostat with Modulating Boiler - Control Conflict??

[billy_bob]

Hello,

I'm using a chrono-proportional thermostat with a modulating combi boiler. I've read that this set up may not be efficient because of a conflict with the inbuilt boiler control logic and the TPI control, (return temperature and stuff I don't really understand). I've also read the chrono-proportional control can reduce boiler life because of excessive switching.

I have a Vaillant Ecotec Pro so I'm considering getting a Vsmart fitted.

Any advice welcome.

 

[ReganAndCarter]

I don't like CP/TPI stats. They seem to work in some situations, but when I fitted a Honeywell for myself with this system some years ago, it was forever turning the boiler on and off. Either it would go past it's set temp or stop before it. Can't quite remember, but it drove me nuts. Don't know if it was saving me money, but as you say, boiler was firing up and shutting down a lot. I took the Honeywell out and fitted a Drayton Mistat. In the settings, it can either be made to work as CP/TPI or as a traditional on off stat.

 

[Dan Robinson]

the settings, it can either be made to work as CP/TPI or as a traditional on off stat.

So could the Honeywell

 

[ReganAndCarter]

So could the Honeywell

No, the CM927 is TPI only. You can play around with the cycles per hour, but it's TPI or nothing.

Maybe you were thinking of another Honeywell?

 

[D_Hailsham]

I have had a Honeywell TPI programmable stat for 11 years and it's brilliant. The room temperature stays as steady as a rock. It also comes on automatically at the appropriate time each morning, dependent on how cold it is. (That's not TPI related).

 

[Dan Robinson]

Maybe you were thinking of another Honeywell

it's brilliant. The room temperature stays as steady as a rock.

It also comes on automatically at the appropriate time each morning, dependent on how cold it is. (That's not TPI related)

Quite right. I have been fitting them as compensated controls for so long I'd forgotten that TPi was not switch off able. I was thinking of the 8P and 8:Su functions. But as with Mr Hailsham, I've not, and to my recollection, none of my customers had a problem with TPi.

Optimisation has caused a few issues in very old creaky houses where the random seeming on/off times upset the natural rhythm of the occupants in relation to the noises the system made when it came on and off.

 

[D_Hailsham]

I have been reading up on "Boiler Plus" and found that TPI thermostats do not meet the load compensation requirements.