Want to learn a bit about thermostats (Vokera Linea HE).

12 Jul 2012
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United Kingdom
Evening All,

So I have a Linea HE with no thermostat (or junction box for that matter). I've done a bit of research and I think I get how "standard" thermostats work. From what I understand they have something called a 'bimetallic strip' which is basically a metal strip that bends when it reaches the required temperature and as it bends it breaks the circuit and turns off the boiler. Then as it cools it goes back into place and makes contact and turns the boiler back on until it reaches the required temperature. This makes perfect sense to me.

Now what I can't make sense of is how this ties up with the boilers settings and the hot water.

My boiler has 4 settings:

WINTER - Heating and DHW functions enabled with DHW pre-heat and SARA BOOSTER function active.

SPRING - DHW only enabled, DHW pre-heat disabled.

SUMMER - DHW only enabled, DHW pre-heat disabled, TSC function enabled.

AUTUMN - Heating and DHW functions enabled, DHW pre-heat disabled, SARA function active.

Am I correct in assuming that if a thermostat was installed it has no baring on which mode is selected? So basically the thermostat would just turn on which ever mode is pre-selected when the circuit is complete? I take it with a combi boiler (as long as the corresponding setting is set) the hot water part is always active regardless? So even with the circuit broken there will always be hot water to the taps?

My other thought is the boiler has two dials, one for hot water temperature and one for heating temperature. I take it the heating one is a little redundant if you have a thermostat installed? Or is it simply if you have your heating set at a higher temperature (on the boiler), the water going through your radiators would be heated to a higher temperature so you would reach your desired temperature on the thermostat quicker as a result (I assume at the cost of more gas).

Sorry if these questions are a bit idiotic just contemplating options for a thermostat in a new house I’ve moved into and want to have a better understanding of the whole system (as you may notice I’m a bit ignorant to the whole thing and I'd rather not be).
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Basically it works as you have assumed - room thermostats are just an on/off switch. This applies regardless of whether it's an old type with a bimetallic strip for £10, or the latest 'smart' effort costing £100s.

Heating temperature is how hot the water going to the radiators is as it leaves the boiler. For older non-condensing types it may as well be set as high as possible so the system and the rooms heat up quickly.
For more modern condensing boilers it should be set to ensure the boiler is in condensing mode as often as possible - usually this results in a lower water temperature and perhaps a longer time to heat the rooms, but uses less gas. Some may install larger radiators than required to achieve the lower flow temperature while keeping a similar heat output.

In either case it is totally unrelated to the room thermostat.
What the boiler does with it's various modes is also unrelated.

Not having a room thermostat will waste substantial amounts of gas, and one should have been fitted when the boiler was installed.

The DHW preheat is a function which wastes gas to keep the boiler hot, so that when turning a tap on you get hot water more quickly.
Without this it will take longer for hot water to arrive at the tap, and this wastes water instead.
The solution to not wasting gas or water is to sling the combi boiler into a skip and fit a proper hot water system.
Flameport, thank you for confirming my understanding of the system is correct and for clarification on the domestic hot water system.

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