Confused about Room Thermostat

[Milleniumaire]

Hi,

I've just had an excellent plumber/heating engineer round to have a talk about replacing my existing combi boiler.

We agreed that the best solution for my 5 bed/3 bath house would be a system boiler + unvented cylinder.

As a Worcester Bosch installer he recommended the 30cdi and either a 210 or 250 litre unvented cylinder, make to be decided, but I'll probably go for either the Vaillant uniSTOR or Santon Premier Plus (maybe the Plumb Center centrestore version). I think the Megaflow is just a little to expensive for what appears to be no benefit over the others.

One thing that confused me was that he said he would need to replace my existing programmable room thermostat (a 7 day digital Honeywell) with a non-programmable thermostat.

I did question him further about this and got the impression that the boiler/cylinder came with the required controls and so the programmable thermostat wasn't needed.

My understanding is that the boiler will have a programmable timer to control the times that the boiler heats up the water and the cylinder will have a similar timer to control it's heating.

Surely the point of a programmable thermostat is that it can regulate the temperature at different times of the day without having to turn the boiler off!

My current old Saunier Duval boiler has one of those circular analogue type switches, which is always switched to constant so the boiler is always on, and is therefore controlled by the programmable thermostat.

Am I missing something?

 

[gassafeengineer]

he will be fitting a twin channel 7 day time clock either in the boiler or external to the boiler this will operate the time in which the boiler comes on and goes off for hot water and heating and your programmable room stat will be changed for an ordinary room stat


You could use ur existing prog stat to operate heating and a single channel 7 day time clock to operate hot water

personally i dont like the programmable room stats but thats only my opinion

 

[Milleniumaire]

So, the twin channel 7 day time clock will control when the boiler and the cylinder are on and off.
This would be useful for the cylinder, although surely the point in using a cylinder is to have stored hot water, not stored "warm" water, so I assumed it would be on all the time, maintained at a constant temperature. Why would I want to turn the boiler off at any time, surely when it is off the house will cool down until it is turned back on.

This is why I currently have the boiler on constant i.e. always on. The programmable thermostat is then set to change the temperature at different times of the day i.e. warmest in the morning and evening (when I'm in), not as warm during the day (when only the wife is in - she can wear a jumper and coolest at night.

As I see it the advantage of using a programmable thermostat is the house never gets too cold as it would if the boiler was switched off for any length of time.

At night, it is off most of the time but if it is particularly cold, it will come on to maintain a minimum temperature. This wouldn't happen if I just used the time clock would it as it would only turn on at a predefined time, not a predefined temperature.

If I changed my programmable thermostat for a manual one I can imagine we would be changing the temperature all the time, whereas at the moment we never need to touch the thermostat (except on those occasions when I'm at home during the day and I want it to be a little warmer).

What is there not to like about programmable room thermostats?

 

[gassafeengineer]

you should of got him to explain better but the cylinder can be on all the time and as it cools down the boiler fires up and heats it up to temperature again once up to temperature the boiler turns off, if you are out all day why would you want the hot water to be on as the boiler is using gas keeping water hot and no one is using it? but yes you can have it on 24/7

as for the heating a prog room stat will not keep the boiler on all day once the room is up to temp the boiler will turn off or if the water temp of the heating system gets up to temp the boiler will also turn off until the system or room temp drops,

with a 2ch prog you can set the times you want the heating to come on and go off and again once the room stat operates the boiler will turn off until temp drops even if clock says its on. or you can have it on 24/7 set stat to 19oc and boiler will go off once temp is achieved and come back on again when temp drops.


you cant turn heating on or off and put it on timed or once like you can with a programmer operations are simpler and easier

 

[mikely]

I can't see any reason why you can't keep your programmable stat. I certainly would, for all the good reasons you have described.

Unless your installer is proposing using one of the advanced controllers from WB described here: http://www.worcester-bosch.co.uk/cache/file/292/technical-information-for-heating-controls.pdf

 

[Milleniumaire]

Mikely thanks for the link - very usefull. It does look like one of the more advanced programmable room thermostats would be useful.

However the guy said he would fit a standard Honeywell thermostat so I'm sure it wasn't one of these.

I'll have to ask him again I think as I'm confused as to why he was so determined to replace my existing programmable room thermostat.