Surely if I reduce the temperature on my combi boiler…

[HairyKitty]

to the slightly more economic slightly lower temperature, it will just take longer for the room to reach the thermostat temperature and therefore the boiler will be running for longer? Resulting in the same or maybe even increased gas use? Anyone know more?

I've been wondering the same, but I'm afraid I don't know the answer. Following your thread with interest though!

Think it’s something to do with if you have a condensing boiler the boiler being set to an eco setting means it uses the condensation or something to heat instead of gas? Probably just talked out my butt but sure it’s something along those lines

Is it not the water temperature people are referring to on the combis. So no point hearing g il the water just to add cold when you run your bath....

i can’t remember precisely what it is but there’s also something about the temp at which the water returns to the boiler being important for efficiency so that needs considering too.

Water temp returning from the radiators I mean, not hot water to taps.

Hey I asked my husband for you

He said

"The most efficient heating temp for
Condensing combi boilers is between 50-55 degrees C

Will reduce gas consumption

The boiler condenses the most at this temp thus giving you the highest efficiency of the boiler"

I think our boiler manual recommends 60 or 65 ish as far as I recall so perhaps it varies with manufacturer.

I must check

Curious about this myself for both heating & water.

I have my water on very hot (it's in the loft, so can't check the actual temp) but turned right up. It's so that I can turn the cold water on fuller & get some kind of water.

I went from a hot water cylinder & shower running off the bath taps to an aqua Lisa & combi & lost a lot of pressure. I tried to get as much info as I could before going to a combi and that style of shower but I'm
gutted there's f'all pressure.

if I drop the temperature, the water pressure will drop further 😢

If your hot water is cooler, then won't you just need more of it to have a hot enough shower/bath/wash?

I get the cooling down hot water theory but I don't see how it helps to make more less warm water if you want the end 'mix' the same 🤪

If your boiler was put in after 2005, it will be a condensing one.

Unfortunately most people have the flow rate set too high meaning that the boiler doesn’t actually work as intended. If you turn down the flow rate it will use less energy to heat your house because the boiler will be working more efficiently. The flow rate does not affect the temperature of the water coming out your taps.

www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature

How would you know what that is?

But won't that mean there's less water pressure in the shower ??

No. You have two lots of water in your house - one flows through radiators to provide heat & the other goes through pipes to taps/showers.

So we’re talking about the flow rate for the water heating your house not for the taps/showers.

Read the link Inposted.

To several posters upthread and the boiler DH, apparently reducing the boiler temp to the eco condensing temp will definitely reduce the max temp of the radiators. In my estimation increasing the time that the boiler needs to be on for to achieve desired temp.

To Boiler DH: are you saying that despite the longer run time, the overall amount of gas used to reach and maintain the required room temp will be fractionally less if the boiler is set to eco?

Again I’d suggest you read the link I posted which gives a good explanation (there’s even a video)

www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature

If you have the flow rate set too high the boiler doesn’t work as it should - it does not condense and therefore uses MORE gas.

Another simple explanation here - it’s physics!

www.heatgeek.com/condensing-boilers-efficiency/

My plumber told me that hot water tanks need to be on at least 60C otherwise there's a risk of Legionnaires disease.

I don’t think people with combi boilers have water tanks. We never have.

We’re discussing boiler flow rates for heating systems- absolutely nothing to do with hot water tanks!

You do have to have your tap hot water fairly hot to ensure it doesn't get too cold going through the system (even if no hot water tank), as legionnaire's can otherwise breed in old side shoots of pipe that have been blocked off.

I think OP is asking about the heating water to radiators, not the hot water system for taps.

I can't see where this answers the question op had in the original post though. Am I missing something?

We got a new boiler in January. I spend ages fiddling around with it at various temps. The eco setting is 68 and the rads never got hot enough to heat the room nicely for the amount of time I had the heating on (only an hour in the am and 3 in the evening). 73 degrees was the perfect temp for us. Maybe if you have the heating on for longer it's more economical but I'm not convinced. I read a lot about condensing and there are mixed opinions. And yes balancing radiators is very important as some heat up faster than others and use the water first so those further away from boiler need to have a higher flow rate. A lot of people just have their lockshields fully open so the heat doesn't actually radiate into the room and the water returns too hot to the boiler.

@BailOutChapsGingersGornSquiffy thanks for the link, I’ve read the article, lots of useful info there.
I’m a bit confused about the boiler type definition - near the start of the piece it says if your boiler is less than 16 years old it’s definitely a combi boiler, but then further down it says “If you have a hot water cylinder, you will have either a 'system' boiler or a 'conventional' boiler (aka heat-only or regular boiler) with a 'vented' or 'unvented' hot water cylinder. The HSE state that hot water must be stored in the cylinder at 60°C to kill legionella bacteria (which can be fatal for humans), which means flow temperatures should be 70°C to compensate for heat losses in the transfer of hot water to the cylinder.”
Ours was installed less than sixteen years ago, indicating it’s a combi, but we also have a hot water cylinder, indicating it’s not?
Am I missing something here or has my poor brain given up the ghost for today?

Are you getting confused with condensing and combi which are two different things. You can have a condensing boiler and hot water tank

Yes.

The title of the op is “Surely if I reduce the temperature on my combi boiler… “ and goes on to hypothesise that doing so would mean the “boiler will be running for longer. Resulting in the same or maybe even increased gas use? Anyone know more?”

The link explains how reducing the flow rate (ie the temperature the boiler heats the water to for the heating system) actually means the boiler works as it’s designed to, so uses LESS gas not more.

Surely that answers the questions concisely.