Combi boiler/thermostat settings

rogertb

Hi chaps, WB Greenstar boiler and I’m getting confused when attempting to keep warm economically … (yes I know me and 60 million others). I have set flow temp to 60 the thermostat reads 16c which I guess is the current temp. In the location of the ‘stat I have set “target” (they call it “permanent”) 18c I only have rads turned on in rooms we’re using and we’re well insulated and d/glazed. The smart readout suggests we’re spending £1.20 an hour. Does anyone know if this is normal ? 

Nebulous2

I'd expect it is normal for very cold weather, should reduce from £1.20 an hour once the temperature of 18c is reached. 

How did you decide on the 60c output temperature? 

I've a WB 8000 life boiler, less than two years old. I've read on here that it is worth reducing the outflow temperature to 60c to increase efficiency as it will condense more effectively. I reduced it to that about two weeks ago. 

I read the manual yesterday however and it said to set the output temperature at 72c and set it up with a 20c drop in the radiators / pipework giving a return temperature of 52c. 

The spec sheet says it is 88% efficient at 72c which it says is a high energy setting, but set for low energy output of 37c it will be 98% efficient. 

So I'm also confused about what I should be doing, but think it will require some experimentation to find an optimum setting. I need to work out a way of checking the return temperature. 

lohr500

@ Nebulous2 I use a couple of these low cost pipe thermometers to monitor the flow and return temperatures on our oil boiler :

https://www.brannan.co.uk/product/clip-on-pipe-thermometers/

Available from a number of online sources at around £10 each.

The theory says that condensing boilers should start condensing at 54c, so the return temperature should be below 54c to start seeing a marked improvement in efficiency. Graph below copied from urbanplumbers website.



I have found with our central heating that our old house gets warm reasonably quickly from a cold start and can maintain the set 18c room stat temperature on even the coldest days with a flow of 60c and a return of 40c.
From the graph you can see that the theoretical efficiency with a 40c return is 94% vs +/- 89% at 52c.

If I were you, I would invest in a couple of the thermometers in the above link and try to get a 60c flow/40c return. To achieve this does need some experimentation. In my case, I had to play around with the boiler thermostat setting, the circulation pump speed and balance the flow through some of the radiators. 

It isn't an exact science as internal and external temperatures affect the rate of heat loss around the circuit, so the return temperature does fluctuate. (Our boiler is an oil one and doesn't have the capability to modulate or operate any automated form of weather compensation). But nearly every time I check the thermometers I am seeing the 60c/40c figures.

rogertb

Thanks Nebulous, glad I’m not the only confused one
I’ll try RTFM again as I don’t understand “return temp. 52c”

matelodave

The optimum setting is the lowest that you can get it commensurate with keeping you warm enough and having reasonable reheat times.

Generally running it a bit longer at a lower temperature is more efficient and cheaper than having it blasting out heat at full bore. Don't get hung up on precise temperatures, just use then as a guide.

One of these will indicate your return temperature - https://www.amazon.co.uk/Clip-pipe-thermometer-hot-water/dp/B00GYV0L5I but one of these would be better as you can measure both the flow and return temps at the same time https://www.amazon.co.uk/Thermometer-Thermocouples-Temperature-Thermocouple-Agriculture/dp/B07923Z2VK/ref=sr_1_13?keywords=differential+thermometer&qid=1670834996&sr=8-13

If you are looking at the smart meter IHD then that isn't everso good at giving you precise info, especially for gas. 

It only updates once every 30 minutes, it may not have the correct tariff set and bear in mind that the boiler will be working at full bore for the first hour or two to get the house up to temperature when the thermostats will then control it. 

For more precise monitoring you need to read the actual meter (the one that's fixed to the incoming gas mains) 

Nebulous2

rogertb said:

Thanks Nebulous, glad I’m not the only confused one
I’ll try RTFM again as I don’t understand “return temp. 52c”

Flow temperature is the temperature your boiler heats the water to, before it pumps it around your house to the radiators. Return temperature is the temperature it returns back to the boiler, after its journey round your house. For a more efficient system you want the return temperature to be under 54c. Unfortunately the boiler doesn't measure that temperature, so you need to work it out for yourself. 

[Deleted User]

I’ll try RTFM again as I don’t understand “return temp. 52c”

Hot water circulates around your radiators. As heat is emitted from your radiators, the water flow loses temperature. By the time that a given volume of water returns to the boiler it will be at a lower temperature than when it left the boiler PROVIDED your system is properly balanced.

This link is worth a read:

https://www.theheatinghub.co.uk/why-our-condensing-boilers-do-not-condense

Nebulous2

lohr500 said:

@ Nebulous2 I use a couple of these low cost pipe thermometers to monitor the flow and return temperatures on our oil boiler :

https://www.brannan.co.uk/product/clip-on-pipe-thermometers/

Available from a number of online sources at around £10 each.

The theory says that condensing boilers should start condensing at 54c, so the return temperature should be below 54c to start seeing a marked improvement in efficiency. Graph below copied from urbanplumbers website.



I have found with our central heating that our old house gets warm reasonably quickly from a cold start and can maintain the set 18c room stat temperature on even the coldest days with a flow of 60c and a return of 40c.
From the graph you can see that the theoretical efficiency with a 40c return is 94% vs +/- 89% at 52c.

If I were you, I would invest in a couple of the thermometers in the above link and try to get a 60c flow/40c return. To achieve this does need some experimentation. In my case, I had to play around with the boiler thermostat setting, the circulation pump speed and balance the flow through some of the radiators. 

It isn't an exact science as internal and external temperatures affect the rate of heat loss around the circuit, so the return temperature does fluctuate. (Our boiler is an oil one and doesn't have the capability to modulate or operate any automated form of weather compensation). But nearly every time I check the thermometers I am seeing the 60c/40c figures.

Thanks very much. It's good to see that graph matches the figures on the spec sheet for my boiler. I think I do need to invest in a pipe thermometer.

We are at -5c outside today and my heating is struggling to get up to 18c for the first time since I turned the flow temperature down. I'm in a very old stone house and I'm not allowed double-glazing, so sash and case single glazing with cheap secondary-glazing (plastic sheets secured with magnets) inside it. 

[Deleted User]

It's good to see that graph matches the figures on the spec sheet for my boiler.

The graph applies to all condensing boilers: it is based on basic physics.

If I were you, I would invest in a couple of the thermometers in the above link and try to get a 60c flow/40c return.

That requires the owner to balance the heating system. Playing around with the boiler set temperature will not achieve a 20C differential.

https://www.bestheating.com/info/a-best-heating-guide-how-to-balance-radiators/?gclsrc=aw.ds&gclid=EAIaIQobChMI_IC_nN7z-wIVDuR3Ch2RmQjgEAAYASAAEgJ2gPD_BwE

70sbudgie

A few points:

I also have a WB Greenstar and haf a quick look through the manual last night. It suggested that when setting the flow temp, it has a function that lets you know when it is more efficient (ECO pops up on the screen). I am just working myself up to going out in -4° to go and check. I'm guessing it must be to do with how the system was set up when the boiler was installed.

Also, I understand that it is possible to get double glazed sash windows. But they're not cheap. (I'm guessing that you may be in a conservation area and that you have to retain the sash windows for that reason). Would thick / thermal curtains be an option, as they would help? I notice the difference even with our modern double glazing.

rogertb

Yes we’re at -2 at the moment, flow temp 60 ‘stat reading 17 target being 18c. The boiler stops output sometimes even when the stat is at 17 (ie not reached 18)
but, same as Nebulous, it seems to struggle to get to 18 … maybe that’s because of low flow temp (60 when manual suggests 65) I’ll check it out today, record cost and maybe raise it to 65 tomorrow. BTW thanks for all the contributions, this site has such helpful members.