How to optimise your combi boiler

robj20 · 5 Sep 2022 at 17:36

jpaul said:
optimum temperature with the condensing boiler and big rads is 45 outgoing not 25 ? and then hoping for a 20C @return.

with a combi boiler(no tank) it is the water heating duties that demand a high Kw boiler - mines 30 but I'd hope it is only using <5 to heat the house on a <5C day
and 5 * 5p/gas/kwh* 12 hours a day would be £3/day.

You just need the return temp to be below I think around 53c. But I think lower flow temps have an advantage in that you just use less gas the less your heating the water.
Better for the boiler to be on 100% of the time at 25c than 50% of the time at 50c.

Mysterae_ · 5 Sep 2022 at 18:22

Mickie said:

Good channel that one, has a few other interesting videos too, thanks for sharing.

I see that he poo poo's the Hive system (in another video) because it doesn't have any modulation control due to having no outside temperature or live weather monitoring. This is understandable but not everyone has a modern boiler that allows this, but it's something to look for when thinking about upgrading. A major benefit of the Tado system I believe is the ability to modulate with outside temps, so I may well replace the Hive with Tado when the time comes to replace the oil boiler. It's a shame the Hive doesn't have this, seems like it would be an easy upgrade for the developers too.

I'm in the middle of getting my heating system sorted and ready for the winter, just ordering parts now. It's a convoluted system with an oil boiler, biomass (wood) boiler and a huge 3,000L accumulator tank. I might do a thread here if it's of interest to anyone.

Tinders · 5 Sep 2022 at 19:27

Standard boilers just effectively on off contact. Its the opentherm ones that have better control. Ultimately its the burner in the boiler that defines efficiency, higher turndown ratio's define the modulation range, you also have combustion optimisation built into the boiler control that can help.

I'd say the best thing we could all do is drain and flush our heating systems, if it hasnt been done in the last 2 years, makes a huge difference. The biggest efficiency gain im my house will be to remove women, i have my mom, my wife and 2 daughters, none of whom have a scooby doo about thermostats

Richie · 5 Sep 2022 at 19:59

dirtychinchilla said:
Nice! That definitely sounds like weather comp.

Yeah I just looked it up and it's the OS2 sensor which is the "Outside Sensor" for weather compensation:

A quick Google suggests that the boiler (Ideal Combi ESPI 35) is also OpenTherm... I have a 34e gen Nest Thermostat on it just now so I'm wondering how difficult it would be to get it to use OpenTherm....

Currently both thermostats are connected via a wiring center and some danfoss valves.

jpaul · 5 Sep 2022 at 20:59

On OpenTherm, it does appear the system itself is not collecting data on gas usage , or using that to optimise the boiler output , so it's a bit open loop ?
so if you wanted to compare having the living room at a constant temperature versus changing it at different times of the day, you are on your own ..
it's a start though.

Richie · 5 Sep 2022 at 22:30

I'm not sure if I can use OpenTherm as my heating set up uses 2 nest thermostats as it is a double zone system.

Any advice on the following which I have pulled off the owner manual:

EFFICIENT HEATING SYSTEM OPERATION

The boiler is a high efficiency, condensing appliance which will automatically adjust its output to match the demand for heat. Therefore gas consumption is reduced as the heat demand is reduced.

The boiler condenses water from the flue gases when
operating most efficiently. To operate your boiler efficiently (using less gas) turn the central heating temperature knob (B) to the ‘E‘ position or lower. In winter periods it may be necessary to turn the knob towards the ‘MAX’ position to meet heating requirements. This will depend on the house and radiators used.
Reducing the room thermostat setting by 1ºC can reduce gas consumption by up to 10%

WEATHER COMPENSATION

When the Weather Compensation option is fitted to the system then the central heating temperature knob (B) becomes a method of controlling room temperature

Turn the knob clockwise to increase room temperature and anti-clockwise to decrease room temperature. Once the desired setting has been achieved, leave the knob in this position and the system will automatically achieve the desired room temperature for all outside weather conditions.

Currently I set the CH boiler dial to "E" for the efficiency mode but, if I'm reading the weather compensation section correct, I should set the temp to the room temp but this range is 30oC to 80oC and my room temp on the Nest will be 18oC... "E" mode puts it at 68oC.

Slightly confused as to what to set it to :confused:

User manual can be viewed here - https://idealheating.com/uploads/documents/logic-combi-esp1-user-guide.pdf.

.

Mickie · 5 Sep 2022 at 22:53

The zones are controlled by switches from the two thermostats. So annoyingly you can’t use the open therm nest thermostats with the boiler. You can only use them as basic switches.

I’m not sure if weather comp works with zones.

Richie · 5 Sep 2022 at 23:03

Yeah I guessed you can't use OT as it's zone valves. It's currently setup as basic switches into the wiring centre to control each 2 port valve (I just modified the wiring centre wiring).

Be a bit daft if the weather comp doesn't work with zones as this is the system the house builder put in when new so should work.... I'm just not sure what the manual means about turning the boiler CH temp to be the room temp as the lowest it goes is 30oC!

andy_mk3 · 5 Sep 2022 at 23:11

Just checked mine while I remember, was set to 70C! Knocked it down to 55C. It should help a lot I'm hoping, I found last winter (our first winter here) that the house heated up very quickly and often overshot the set temperature. Hopefully bringing that down will help in both control of temperature and efficiency.

Uther · 5 Sep 2022 at 23:17

andy_mk3 said:
Just checked mine while I remember, was set to 70C! Knocked it down to 55C. It should help a lot I'm hoping, I found last winter (our first winter here) that the house heated up very quickly and often overshot the set temperature. Hopefully bringing that down will help in both control of temperature and efficiency.

I did the the same earlier when I saw the video! Mine was set at 70C too.

dirtychinchilla · 6 Sep 2022 at 08:32

andy_mk3 said:
Just checked mine while I remember, was set to 70C! Knocked it down to 55C. It should help a lot I'm hoping, I found last winter (our first winter here) that the house heated up very quickly and often overshot the set temperature. Hopefully bringing that down will help in both control of temperature and efficiency.

One other issue you might experience is that the heads on your TRVs are slow to react. How old are they? If old, consider replacing them with a liquid thermostatic head. They respond a bit quicker and are less prone to death than the gas equivalent.

andy_mk3 · 6 Sep 2022 at 08:38

dirtychinchilla said:
One other issue you might experience is that the heads on your TRVs are slow to react. How old are they? If old, consider replacing them with a liquid thermostatic head. They respond a bit quicker and are less prone to death than the gas equivalent.

House is only 5 years old so shouldn't be an issue there I don't think.

Jimbo Mahoney · 10 Sep 2022 at 14:56

Currently optimising my system before the winter.

I've fitted a tempetature sensor to the output and return to my combi boiler - I'm looking to balance the radiators so that the return temperature is as low as possible.

Approx. efficiency on a condensing gas combi is:

> 54 = non-condensing mode = 87% or less
50 = 90%
40 = 94%
30 = 97%
20 = 99%

Sadly, my system seems pretty poor with the return temperatures, but that's with all the radiators full open. I had hoped that shutting off the bathroom towel rail / radiator would help (they're known to give off little heat, therefore return high temperatures and destroy the condensing efficiency).

Currently = 52'C output and 48 'C return!

Now to hunt for the radiators that are flowing too fast and returning high water temperatures...

Jimbo Mahoney · 10 Sep 2022 at 15:13

Found the main culprits - small radiator in the single bedroom is pretty much returning water at the same temperature, as is the one in the main bedroom.

"Best" one so far is returning 44'C with 54'C input, but even that's pretty poor! It ought to be at least 12 degrees delta, but I am doing this test with an ambient of 22'C..

I've tightened down the lockshields on the offending rads and will re-test when they settle.

robj20 · 10 Sep 2022 at 15:46

Mickie said:
The zones are controlled by switches from the two thermostats. So annoyingly you can’t use the open therm nest thermostats with the boiler. You can only use them as basic switches.

I’m not sure if weather comp works with zones.

Opentherm works fine on mine with Evohome and 6 zones.

Jimbo Mahoney · 10 Sep 2022 at 17:23

robj20 said:
Better for the boiler to be on 100% of the time at 25c than 50% of the time at 50c.

That's not quite right, BUT you have a point.

@ 25'C, return would likely be no less than about 18'C (it couldn't be less than ambient anyway), so boiler would be about 99% efficient.
@ 50'C, return would likely be 35'C, or possibly as high as 40'C depending on the radiators, so boiler would be about 95% efficient.

Therefore boiler would consume 99 arbitrary units @ 100% uptime and 25'C output and 95 * 0.5 = 47.5 arbitrary units @ 50% uptime and 50'C output.

Your point does hold merit however, because:

Lower return temps are better (below 40'C the returns become less significant, but you definitely want to be below 54 'C)
Lower flow temperatures require less gas input
In reality, boiler would not be operating at 100% uptime @ either output

Mickie · 10 Sep 2022 at 21:20

robj20 said:
Opentherm works fine on mine with Evohome and 6 zones.

Evo home doesn't work the same way as zone valves with its own wiring system.

Uhtred · 11 Sep 2022 at 10:37

A couple of years ago we had our boiler and rads replaced. A few months later I found 'urban plumbers' youtube channel where he talks about the things being mentioned in here. It annoys me that I didn't take an interest when the system was being installed because I would have made better design discissions than our plumber did.

I would have chosen a smaller boiler and openthrerm compatible (this should be a mandatory feature for all boilers fitted), I would have gone combi instead of a system boiler, but at the very least fitted a hot water diverter kit so I could run a different flow temperature for the radiators and a higher temp to fill the water cylinder (difficult to retrofit this now). I would have wanted a weather compensation sensor (again this should be mandatory) and bigger radiators. I've reduced the pump speed from highest to lowest but even so my flow/return delta is hilariously bad and there isn't really much I can do about it.

It's sad to think that this plumber was very experienced but wasn't aware, or didn't care, about designing a system to get the best out of the technology available. It's not even that hard. Think of all the energy we've wasted as a country over the decades.

robj20 · 11 Sep 2022 at 10:46

Uhtred said:
A couple of years ago we had our boiler and rads replaced. A few months later I found 'urban plumbers' youtube channel where he talks about the things being mentioned in here. It annoys me that I didn't take an interest when the system was being installed because I would have made better design discissions than our plumber did.

I would have chosen a smaller boiler and openthrerm compatible (this should be a mandatory feature for all boilers fitted), I would have gone combi instead of a system boiler, but at the very least fitted a hot water diverter kit so I could run a different flow temperature for the radiators and a higher temp to fill the water cylinder (difficult to retrofit this now). I would have wanted a weather compensation sensor (again this should be mandatory) and bigger radiators. I've reduced the pump speed from highest to lowest but even so my flow/return delta is hilariously bad and there isn't really much I can do about it.

It's sad to think that this plumber was very experienced but wasn't aware, or didn't care, about designing a system to get the best out of the technology available. It's not even that hard. Think of all the energy we've wasted as a country over the decades.

You don't use opentherm and weather compensation.
Opentherm (load compensation) is much better if you have the option.

I'd say 99% of plumbers haven't much is 8 of the latest systems they still use the default radiator outputs to calculate sizes rather than sizing for a lower flow temperature.
Considering the price of radiators you don't go far wrong with doubling the size of then throughout your house or just fitting the biggest you can fit, using opentherm there isn't really a downside.

Mysterae_ · 11 Sep 2022 at 11:46

I stumbled across this video which illustrates there's a bit more involved when selecting a radiator. It does get a bit technical. An interesting section of the video is at 18:45 where the bloke mentions how we install radiators differently to the Europeans and against design spec costing us efficiency, plus how radiator covers can remove up to 30% output.

I do think with the push for ASHP and required larger radiators (where UFH is unfeasible) the radiator designers should be getting more inventive, making a feature of them instead of the crap ones installed in the majority of houses today. There are some nice vertical type radiators but they rarely have the output required for low flow temps.

I agree with @Uhtred, a lot of installers just fit the most basic they can for the price quoted to the customer and be done. To most, it's a job and nothing more.