Worcester Bosch greenstar 28i junior flow rate/temperature controls

BUFF

spudwood said:

markin said:

You need a way to measure the return pipe temp, To condense and save gas it needs to be under 54c.

So number 3 or just a few mm over should be perfect, And yes it will take far longer to heat but use less gas.

Hi, thanks for this. Do you mean the return water pipe to the boiler? How can I identify this pipe please?

Do you have access to the underside of the boiler (i.e. can you see all the pipes connecting in & out)?
https://library.plumbase.co.uk/flipbooks/RE/worg28i_20996_t/mobile/index.html see p16

spudwood

Hi @vic_sf49 thank you for sending those figures. Your December 22 usage was similar to mine. Were you using the same timings then that you have listed? Also, could you say over a 24 hour period, how long your boiler is actually 'on' for, on average. Thanks!

spudwood

Hi @BUFF, thanks for your reply. How long into running does a boiler start condensing? How long should it be left running for it to be at its most efficient, roughly?

spudwood

BUFF said:

spudwood said:

markin said:

You need a way to measure the return pipe temp, To condense and save gas it needs to be under 54c.

So number 3 or just a few mm over should be perfect, And yes it will take far longer to heat but use less gas.

Hi, thanks for this. Do you mean the return water pipe to the boiler? How can I identify this pipe please?

Do you have access to the underside of the boiler (i.e. can you see all the pipes connecting in & out)?
https://library.plumbase.co.uk/flipbooks/RE/worg28i_20996_t/mobile/index.html see p16

Thanks for this. I will check it out

BUFF

spudwood said:

Hi @BUFF, thanks for your reply. How long into running does a boiler start condensing? How long should it be left running for it to be at its most efficient, roughly?

If the conditions are right pretty much from the start imo.
Your 2nd question is a lot more complicated as it will involve more factors incl. your building, system & how you run it. Generally from a truly cold start it will run flat out for a short period until it starts modulating to demand. To be at it's most efficient (& assuming that your system also has the ability/controls to maximise efficiency) you would want want to run your boiler longer but at the lowest return temp.  However, boiler efficiency & the best daily heating efficiency are not necessarily the same thing as you would also want to run the system in the best way that suits your lifestyle e.g. if you are in all day then you might be happiest to run it all day but at very low temp whereas if you are out all day but want heat quickly when you come back in you are going to want higher flow/return temp for faster response at least to start (at the expense of slightly lower boiler efficiency  % but probably less overall daily gas usage).

spudwood

@BUFF really helpful that, thanks. Can I ask what you mean by 'assuming that your system also has the ability/controls to maximise efficiency' please!

vic_sf49

spudwood said:

Hi @vic_sf49 thank you for sending those figures. Your December 22 usage was similar to mine. Were you using the same timings then that you have listed? Also, could you say over a 24 hour period, how long your boiler is actually 'on' for, on average. Thanks!

It was a bit all over the shop, as my timings were being tweaked a lot. Especially during that very cold 11 days, where I eventually set my thermostat to a higher overnight temp. Changed from 14 to 16.5.

I've split the results into 3 chunks, as there was a big difference in outdoor temps/use.

But per 24hr period in Dec 2022, boiler was actively heating (according to my Hive) for...

1-7 Dec between 3h15 - 4h28.

1-7 Dec average = 3hr44.

8-18 Dec between 5hr12 - 6hr41.

8-18 Dec average = 5hr44.

19-31 Dec between 2hr28 - 3hr 59.

19-31 Dec average = 3hr18.

BUFF

spudwood said:

@BUFF really helpful that, thanks. Can I ask what you mean by 'assuming that your system also has the ability/controls to maximise efficiency' please!

a) your boiler is properly sized for the demand, the ideal would be if your boiler was able to modulate down enough to supply just as much heat to maintain the required temp. as was necessary.
Your 28i Junior is rated for ~25kW output max to CH but I am not sure what the modulation ratio is (I would guess 4 or 5 so minimum output of 5 or 6.25 kW). If e.g. your household only requires 4kW to maintain temp. once it has achieve your required building temp then, if it can't operate at that low level, the boiler would require to cycle ( switch off/on) over time & that is less efficient.

b) that you have programmer, room stat(s), TRVs etc. to maximise the efficient running of the boiler. Part of that is having controls that can interface very closely with the boiler (& possibly take over) to enable very fine modulation of the burn and also use load & weather compensation to minimise gas usage.
Looking at your programmer & the age of your WB you may be in the same situation as I find myself with a similarly aged WB with the same programmer. None of the current WB controls that provide all the above are available for my boiler (mine is 14+ years old) & because WB use a proprietary communication protocol you can't buy a 3rd party controller that does the same either. My room stat is a Class 4 (so it has some intelligence via TPI) but it can't do the truly low level communication/modulation to eke out the last few % of efficiency & it doesn't support load or weather compensation either.

vic_sf49

Brannon pipe thermometer in situ. Decided to hunt out the actual return flow pipe to the boiler, rather than try to get a reading from a radiator valve, as I'm not 100% sure which is the last one on the system.

Flow temp set to 3.5. Return flow is 43 degrees.

I'll see if that flow temp setting is high enough, during these next few days of colder temps.

I might also get some usage figures for a 2 hr period (can't remember if that is this thread, or @spudwood's other one).

Thermometer is sat on a non painted bit of pipe. String is where I'd tied the spring fitting, and thermometer to my wrist, or there was a high chance of me dropping down the back of the boiler's cupboard. Think of a child with a helium balloon.

markin

Whats the actual flow out? Would it be 65c and its a 22c drop?

Checking every rad to find one that's 43c would tell you whats likely the last rad.