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New combi boiler (Bosch); temperatures

Does what it says on the tin
brightncheerful
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New combi boiler (Bosch); temperatures

#403865

Postby brightncheerful » April 13th, 2021, 1:02 pm

Having had a new Worcester Bosch 8000 30 kw life boiler installed, I need to ascertain the most economical temperatures for the central heating and hot water.

We have a 4 bed 3 rec detached house, cavity wall construction, 1999 era loft insulation. The heating is on 24/7.

Usually, we have the hall stat at 20-21C - except when the weather outside is very warm/hot in which case the stat would be around 15 or so - but I gather that's a separate issue to the boiler temperatures. Am i right in thinking that provided the temperature on the hall stat is lower than the boiler temperature the difference is the leeway i have for increasing the hall stat temperature, or doesn't it work like that?

On the Vaillant combi we had before, I set both temperatures at 55C on the boiler. When the installer of the Bosch showed me how to set the boiler temperatures, he entered 70C for the CH and 60 for the water. When I told him that i used to set them at 55C he said that would mean the radiators would not be emitting that much heat - (which might explain why Mts Bnc used to complain that the house wasn't very warm and she would turn up the hall stat; I appreciate that the house insulation and outside temperature are also factors.)

I suggested we have the CH temp at 65 and the water at 55 which is what we have done. However, what is the likely gas consumption difference (in percentage terms) if i were to increase the CH temp to 70? And if the hall stat were at 21C would it make a noticeable difference to the radiator temperature?

As you may have have gathered, it's all a bit beyond me so i need to find a way to understand the basics as I can't keep asking the installers to explain.

tia
Bnc

staffordian
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Re: New combi boiler (Bosch); temperatures

#403929

Postby staffordian » April 13th, 2021, 4:05 pm

An interesting question, which I have found hard to get a definitive answer to, so I too am keen to see what advice ensues.

For myself, I set the water at max, on the basis that with mixer taps and thermostatic mixer shower it can easily be cooled, and I hope it also reduces or eliminates any outside chance of Legionaires disease.

As for the central heating temperature, my understanding is that the condensing part of a condensing boiler, which is what gives it it's supposed efficiency, only works properly if the water returning to the boiler, after passing through the rads, is below a certain temperature. So I keep ours at 55.

Additionally, this relatively low temperature seems to me to even out the temperature variations. I feel, perhaps wrongly, but it seems to work for me, that if the central heating water is much hotter, the rooms will heat up more quickly, overshoot the set temperature (because the rads will still dissapate some heat after the thermostat has switched the boiler off) then cool, with a more pronounced see-sawing of temperature. As you keep your heating on 24/7 then taking longer to reach a certain temperature should not be an issue, and any lack of comfort would be down to the actual setting (or draughts etc) rather thanmthe radiators not being particularly hot.

I'm guessing you have a decent electronic thermostat if you've had a boiler upgrade. If not, and you are relying on an old fashioned rotary mechanical 'stat with a bimetallic strip, the see-sawing will be more pronounced because they tend to be less accurate*. Eg, if set to 21 it might switch off at 22 then not come on again until it falls to 20. We upgraded a few years back to a programmable thermostat and it has made an incredible difference to the usability of the heating and the comfort in our bungalow.

Edit to add: The question you ask towards the end... The hall stat setting won't make the rads any hotter or cooler. That is more or less entitely dependant on the setting a the boiler. All it will do is keep the heating on longer until the hall reaches 21 rather than 20.5


*Accurate is not exactly the right term. There is a specific term of the switching range which escapes me at the moment.

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Re: New combi boiler (Bosch); temperatures

#403953

Postby beseeinyou » April 13th, 2021, 5:02 pm

I have had the same model of boiler for 19 months now, after a bit of initial experimenting I have mine set at 72C for the heating and 49C for the water and just use the hall stat / programmer to suit the conditions, typically set at 23C for 2+1/2 hours in the morning, and 23C for 5+1/2 hours in the late afternoon / evening, and as I say just advance to suit if it gets too cold / hot, 1997 Bryant Homes 4 bed detached, typical newer style house.

Beseeinyou

P.S. Sorry, I've just noticed that you have the 30KW model, it is the 40KW one I have if that perhaps makes a difference to the output settings?
Last edited by beseeinyou on April 13th, 2021, 5:06 pm, edited 1 time in total.

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Re: New combi boiler (Bosch); temperatures

#403963

Postby staffordian » April 13th, 2021, 5:19 pm

reallyveryfoolish wrote:

*Accurate is not exactly the right term. There is a specific term of the switching range which escapes me at the moment.

Hysteresis perhaps?

RVF
Thanks, that's the one :)

Sorry, messed up the quotes...
Last edited by staffordian on April 13th, 2021, 5:22 pm, edited 1 time in total.

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Re: New combi boiler (Bosch); temperatures

#403967

Postby UncleEbenezer » April 13th, 2021, 5:22 pm

ReallyVeryFoolish wrote:
beseeinyou wrote:I have had the same model of boiler for 19 months now, after a bit of initial experimenting I have mine set at 72C for the heating and 49C for the water and just use the hall stat / programmer to suit the conditions, typically set at 23C for 2+1/2 hours in the morning, and 23C for 5+1/2 hours in the late afternoon / evening, and as I say just advance to suit if it gets too cold / hot, 1997 Bryant Homes 4 bed detached, typical newer style house.

Beseeinyou

Sorry, a little off topic, but are you sure 49 degrees is hot enough to kill legionella in your hot water system? (Thinking of bathroom shower heads in particular).

RVF

The water from your shower will mix hot with cold.

49 is ample for most purposes. The exception being a bath, where if you ever want to top it up for a longer winter-comfort soak, you'll want water much hotter than that. Hence 60 as (it seems - my installer set that too) as a default for domestic hot water. And perhaps another exception for washing up by hand.

I don't recollect if I've changed the heating down from the default 70 - I may well have done. I don't keep the place as horribly warm as you lot, and now it's spring (with a lot of heat from the sun) the radiators rarely come on at all, even when (like last weekend) the white stuff comes down outside.

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Re: New combi boiler (Bosch); temperatures

#403968

Postby beseeinyou » April 13th, 2021, 5:22 pm

That's an interesting point RVF, is that still relevant in a combi system with no tanks ?

Beseeinyou

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Re: New combi boiler (Bosch); temperatures

#403970

Postby UncleEbenezer » April 13th, 2021, 5:24 pm

beseeinyou wrote:That's an interesting point RVF, is that still relevant in a combi system with no tanks ?

Beseeinyou

That'll be why traditional British showers run either hot or cold, with no intermediate option! ;)

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Re: New combi boiler (Bosch); temperatures

#403975

Postby beseeinyou » April 13th, 2021, 5:37 pm

Having just looked at the manual you can set the water between 35C and 60C, it would seem a bit peculiar to allow you to set it at a dangerous level would it not?

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Re: New combi boiler (Bosch); temperatures

#403977

Postby Arborbridge » April 13th, 2021, 5:42 pm

My combi is set at 70 for the heating as the default, and 55 for the water. Seems to work fine though whether it's the most efficient setting I have no idea. I'm really impressed with the heating generally (the boiler is an Ideal) and the temperature control varies really within close limits. i.e low hysteresis. The origin of that word sound like it came from the Greek for womb, and hysteria (connected, regrettably, to women etymologically).

I still have to wrestle a bit with the radiator thermostats if I want a really hot bathroom - i.e on bathnights. (Showers, you can keep them - horrid things) I turn off the radiator near the main thermostat and wack up the heating water to 80 degrees, bathroom radiator on 5. With the heated floor on, it's hot enough even for me!

Arb.

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Re: New combi boiler (Bosch); temperatures

#403987

Postby AF62 » April 13th, 2021, 6:36 pm

staffordian wrote:I'm guessing you have a decent electronic thermostat if you've had a boiler upgrade. If not, and you are relying on an old fashioned rotary mechanical 'stat with a bimetallic strip, the see-sawing will be more pronounced because they tend to be less accurate*. Eg, if set to 21 it might switch off at 22 then not come on again until it falls to 20. We upgraded a few years back to a programmable thermostat and it has made an incredible difference to the usability of the heating and the comfort in our bungalow.


I thoroughly agree with this - many years ago I changed the old fashioned rotary mechanical thermostat with a Honeywell digital programable thermostat - night and day difference in comfort.

However that improved comfort might also have resulted from me moving the thermostat from the hall to the living room (it was a wireless thermostat so I could put it anywhere); I removed the radiator thermostats in the living room. I could never really understand the reasoning for putting the thermostat in the hall - an area I want to be a lot cooler than the living room and slightly cooler than bedrooms, but influenced by the cold when you open the front door or heat from the kitchen.

A few years back I then replaced the Honeywell digital programable thermostat with a Hive thermostat to give me the ability to turn it on and off remotely and also be able to see the temperature at home and receive low temperature warnings. As it is connected to Google Home now means I can turn up the heating on a cold morning from under the duvet in bed just be telling Google to turn the thermostat up!

Whether it is more energy efficient or not, I don't know. What I do know is the house is always a comfortable temperature and the bills are not extortionate.

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Re: New combi boiler (Bosch); temperatures

#404010

Postby csearle » April 13th, 2021, 8:45 pm

AF62 wrote:I could never really understand the reasoning for putting the thermostat in the hall - an area I want to be a lot cooler than the living room and slightly cooler than bedrooms, but influenced by the cold when you open the front door or heat from the kitchen.
My (limited) understanding of the reasoning is that the thermostat is normally placed in the coolest place so that the heating turns off when even that place is warm enough. Then to prevent individual areas overheating thermostatic valves are used to cut off heating locally.

If you put the thermostat in one room and dispense with the thermostatic valves then you make it just fine in that one room but once that room is up to temperature no-one else can get any heat in other rooms.

In my flat the thermostat is in the living room and my office was almost always too cold. For this reason I now have a Hive portable thermostat that I can take with me from room to room if I am fussed*.

Chris
*The room stat in the living room is adjusted so that is always calls for heat so the Hive, which is in series, has complete control.

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Re: New combi boiler (Bosch); temperatures

#404021

Postby brightncheerful » April 13th, 2021, 9:46 pm

I'm guessing you have a decent electronic thermostat


yes, we got it with the new boiler: it's wireless but we had it fitted where the old stat was.

I hadn't realised that it's in the hall because that's the coolest place to warm up and hence the other rooms would at least be on a par. So far, as i write for example, the hall isn't as warm now as earlier during the day. Having just touched the radiator in my office, it's almost cold. I've just turned the stat up 0.5C which triggered the pump and warmed my office radiator.

All the rads in the house, except two (the hall and my office), have TRVs, most of which are permanently on at just below maximum setting. I shall check them all tomorrow to ensure we are not over- or under-heating any of the rooms. when the boiler was installed, all the rads were drained and then checked for efficiency - nifty hand-held device.

i haven't had the system power-washed as the installer concluded wasn't necessary but it's an option that I could have done within 3 months of the installation.

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Re: New combi boiler (Bosch); temperatures

#404051

Postby AF62 » April 13th, 2021, 11:10 pm

csearle wrote:
AF62 wrote:I could never really understand the reasoning for putting the thermostat in the hall - an area I want to be a lot cooler than the living room and slightly cooler than bedrooms, but influenced by the cold when you open the front door or heat from the kitchen.
My (limited) understanding of the reasoning is that the thermostat is normally placed in the coolest place so that the heating turns off when even that place is warm enough. Then to prevent individual areas overheating thermostatic valves are used to cut off heating locally.

If you put the thermostat in one room and dispense with the thermostatic valves then you make it just fine in that one room but once that room is up to temperature no-one else can get any heat in other rooms.


But if, say, I want the hall to be 19c and the living room to be 21c then I have to ensure the radiators in the living room deliver more heat for that area than the area that the radiators are heating in the hall - so that is guesswork if that will work.

I might get lucky so the balance of the radiators in the two areas might work in October when the heat loss from the living room is not significant through the large windows and french doors, when compared to an internal hall with no windows and only an insulated front door. However if it works in October it isn’t going to work in February when there is far more heat loss in the living room.

It also isn’t going to work very well at both weekends and weekdays when the occupation of the home is different, where during the week you might want a fast rise in temperature of a large cold living room as people come home from work, but the quickly heating smaller hall doesn’t need that.

Sure you have the same balance to strike with a thermostat in the living room to keep the hall at a lower temperature. However if you get it wrong the worst that happens is the hall is warmer than you want, which is a waste of money and heat. But it isn’t uncomfortable which is the situation with an under heated living room - and that situation is likely to be as expensive as people then go fiddling with the thermostat!


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