Best temperature setting for combi boiler ?

MikeE67

I expect that this question is rather like the question "How long is a piece of string?" but I will ask it anyway!

What are the best water temperatures for heating water and central heating?

I have a Vaillant ecoFIT pure combi boiler.
The water heating temperature goes from 35C to 60C 
It is currently set at 48C as my girlfriend says that setting it to 60C burns her hands when she runs the hot water tap!
I know that 60C is recommended because of the threat of Legionnaires disease, but is it really that important to set it at 60C?

The central heating temperature goes from 10C to 75C.
It is currently set at 75C because my girlfriend feels the cold!

I am thinking along the lines of energy efficiency as mine is a condensing boiler.
I have only had it installed a few weeks ago. I was using an old Ideal Classic boiler which was over 25 years old and very inefficient at around 75% compared to 95% now.

Thanks in advance for any advice.

FreeBear

Legionella is only a risk if you are storing hot water (i.e. in a HW cylinder). With a combi boiler, the water is heated as it flows in from your mains water supply. The incoming water will be pretty cold (around 8-10°C in winter) - At this temperature, the Legionella bacteria can not survive any appreciable length of time, and the water company would have treated the water to eliminate the risk.

Set the HW temperature to 50°C, and you'll be fine. It will reduce the risk of scalding and improve the life of the boiler - The higher temperature you heat the water to, the more lime scale is deposited in the heat exchanger. You'll also save a few bob on gas too.

JohnB47

MikeE67 said:

I expect that this question is rather like the question "How long is a piece of string?" but I will ask it anyway!

What are the best water temperatures for heating water and central heating?

I have a Vaillant ecoFIT pure combi boiler.
The water heating temperature goes from 35C to 60C 
It is currently set at 48C as my girlfriend says that setting it to 60C burns her hands when she runs the hot water tap!
I know that 60C is recommended because of the threat of Legionnaires disease, but is it really that important to set it at 60C?

The central heating temperature goes from 10C to 75C.
It is currently set at 75C because my girlfriend feels the cold!

I am thinking along the lines of energy efficiency as mine is a condensing boiler.
I have only had it installed a few weeks ago. I was using an old Ideal Classic boiler which was over 25 years old and very inefficient at around 75% compared to 95% now.

Thanks in advance for any advice.

The installers of my recently fitted combi have set the domestic hot water temperature to 52C and the CH temperature to 72C.
The water temp is a bit lower than our old boiler but fine by us - probably a more appropriate temp.
As for CH temperature - I think it's best to think more about the setting on your room thermostat. Ours is set to 21.5 and the heating is 'on' from 7:30 morning to 17:00 (log burner after that). It purrs along nicely, hardly making the rads warmer than tepid after the first hour or so. I think it wouldn't make much difference if I changed the CH temp to anywhere from 70 to 75.
How about seaching on-line for your particular boiler manufacturers recommended settings for CH temperature?

As for legionnaries desease - I think the recommended min temperature is more for system boilers - where hot water is stored in a cylinder. A combi supplies hot water 'on demand', so I thing Legionnaires wouldn't be a factor. (Although I'm not an expert).

Carrot007

Hot water tap?

Sorry but you have a hot water tap?  Just the one? ;-) Seriously though get muixers for everything. Seperate taps had a puporse years ago. Today they need resigning to history. And yes you can still burn yourself, but you have to be more silly!

As for the boiler. Yes for condensing the highest temperature is the best. Turning it down is a bad idea. Just use the room thermostat to set the house temperature.

As for FB's thought's yes heat does cause scale. The heating loop should have some inhibitor in it though, so not heating issues. The heat exchanger can actually be cleaned if you can find a gas engineer who can actually think for themseves and not just follow the flow chart manual! Had that on a boiler in 2010ish I think, Had joind one of those smonthly pay things. Was the third or forth guy before they actually took it out and cleaned it in limescale remover. Worked fine with no issues for another 5 years after that (maybe more, I moved!)(and the engineering by multiple choice manual would have just said repalce everything!). (And I agree Legionella is only a issue for cylinders, Or very small for a tap that is used every year or so! But may as well keep high and have mixer taps IMO. Hey ask your yearly indi boiler checker if they can do a heat exchanger clean every 5 years, not usually hard and like I say can be done!).

Norman_Castle

MikeE67 said:

The central heating temperature goes from 10C to 75C.
It is currently set at 75C because my girlfriend feels the cold!

I've found a high boiler temperature gives a varying room temperature. Mines set to about 58 which gives a consistent temperature. A lower boiler temperature will still heat rooms to a higher thermostat temperature.

Start by setting the trv's to halfway which is 70 degrees then adjust up or down over time in small amounts to get the right preferred room temperature.

Norman_Castle

Carrot007 said:

Hot water tap?

Sorry but you have a hot water tap?  Just the one? ;-) Seriously though get muixers for everything. Seperate taps had a puporse years ago. Today they need resigning to history.

I prefer separate taps.

matelodave

this is from the Viesmann website

"A condensing boiler is one of the most efficient types of boiler. This is because it is able to recover virtually all the heat from the flue gases and use this to heat your home. For the boiler to work at its most efficient, the heat exchanger needs to be equal to or below the dew point temperature. The dew point temperature is a measurement that determines the humidity of air and is the temperature at which water droplets form in the heat exchanger. For gas boilers, the dew point is around 55 °C. This means that the water needs to be 55 °C or lower for your boiler to maintain its efficiency". 

Running it longer at lower temperatures will save energy compared to higher temperatures when the boiler may have to keep heating and cooling. Think of it a bit like driving - blatting up the M1 at 80 will use a lot more fuel than doodling along at 50 - it may take a bit longer but you'll still get there and save yourself some money.

The same with your boiler, turn it down to the point where it takes too long to reheat the place and then turn it up a bit (50-55 should be about right). The boiler temp controls the time it takes to heat your room, whereas the room stat controls how hot the room gets assuming that the boiler temp is high enough

It's also worth bearing in mind that every time you turn on the hot tap, the boiler will crank it'self up to full blast sending quite a bit of heat up the flue before the water gets hot so the less often you use it the more energy you'll save. So try to avoid short draw-offs to rinse your hands and stuff as it wastes both water and energy - use cold when possible.

MikeE67

I didn't think of googling my boiler manufacturers recommended water temperature settings!

I just did that and got 60C for the hot water and 75C for the central heating.

Seems a bit too hot for me and not that energy efficient but what do I know ?

Thanks to everyone for their feedback.

Edit: I didn't know about Legionnaires disease not being a problem with a combi boiler. Cheers

Talldave

For maximum efficiency you need the return flow temperature of water in the CH circuit to be down to 45C.  I've therefore seen it suggested that 65C for CH, with a 20C drop flow to return, will achieve this.

[I'm not a qualified heating engineer - it's just what I've read online]

MikeE67

Talldave said:

For maximum efficiency you need the return flow temperature of water in the CH circuit to be down to 45C.  I've therefore seen it suggested that 65C for CH, with a 20C drop flow to return, will achieve this.

[I'm not a qualified heating engineer - it's just what I've read online]

Ok I will try that thanks.
60C is too hot for hot water for my girlfriend anyway!

daveyjp

Hot water and CH circuits both on 50 degrees.