Evening all, well after much searching and interesting reading I have resorted to my first post. Just to be clear, my plumber is fitting my boiler but I get the impression it has been a little while since he fitted one, so I have a few questions.
The boiler is a grant eco vortex utility standing boiler with a sealed system kit.
We have bought a Honeywell CMT 927 and two motorised valves V4043H.
Now plumber said that room thermostat is in the CMT 927; I get this!
However, I am not clear on whether I need a cylider thermostat; he thinks not? Any thoughts?
Also, the CMT927 appears to be solely for controlling room temperature (central heating on/off time) is this correct? How should I therefore control the switching on and off of the hot water. The wiring diagrams indicate a "programmer" is needed, so do we need something over and above the CMT927 to control when the water comes on......or is it instant because it is now a sealed system?
(Brave man making his first post on boilers etc - but if you have read some of the archives you probably know what to expect ;-)
So an oil fired floor standing condensing boiler basically...
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a couple of 2 port zone valves...
Yup - it is a combined stat and timer. By combining them you get the ability to have it select different temperatures for different times of the day.
Since you are going for an S Plan arrangement[1] by the sounds of it, then yes you will need a cylinder stat. Without that there would be nothing to call for heat to get the zone valve to open, or cause the boiler to fire.
[1] See here for a diagram and wiring diagram:
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particular see:
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can follow the function of the cylinder stat in driving the hot water zone valve, and that in turn causes the boiler to fire when required.
I believe so, yes.
Yes you will need a programmer. A simple time switch type would be fine. That and the cylinder stat will then control when the water is heated. Many are two channel (i.e. designed to time operation of the heating and the hot water - however if you have a prog stat you don't actually need separate time control of the heating. However there is nothing stopping you having both - you could actually just leave the heating setting on the programmer to "always on" and let the room stat do the rest for the heating.
The fact that it is a sealed system has no bearing on it - it only describes a heating system that does not require a header tank.
Background on sealed systems:
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"Instant" hot water is often provided via "combination" or "combi" boilers. Most combis also use sealed systems (a few don't), but the reverse can't be inferred.
John, thank you for your very comprehensive response. I have spoken to the supplier and am returning the programmeable room stat with a 2 channel programmer, wireless room thermostat (no programmer) and a wireless cylinder thermostat.
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