Explanation of thermostat vs control temp

[JonathanM]

Its being turned into flow water at 45C because the flowwater which was at 55C is giving up its heat to the rads and the reason that its not going any lower is because the burner is cutting back in at 45C (SP-5C) due to the anti cycle time being too short, it then short cycles as the OP states until it drops still further, IMO it has to fall to ~ 34/35C to stand a good chance of getting away on the first fire up after burner shutdown.

Oh, I see now. I had misunderstood. So how can that sort of return temperature be achieved within the anti-cycle time?

EDIT: We don't know whether both zones are running at the same time, and the status of any TRVs. I'm guessing these things might make a difference?

 

[Johntheo5]

By increasing the pump speed to 100% which will certainly help probably even with TRVs.

 

[JonathanM]

Interesting, one way or the other, a gas boiler is certainly a instant heater since its contents may only be 2 litres or so, at 21lpm, 2 litres will have passed through it in less than 6 secs, the Hx metal will take some finite time to heat up however little but once this has heated up then in less than another 6 secs, the 23kw will be transferring to the water and the burner will almost trip instantly (from water at 45C) but not so from water at 34.3C, this must rise by another 5C to reach 39.3C, with a boiler dT of 15.7C = 55C, burner trip.

I still agree with the general principle, that's it like an instant water heater. But I don't think my 19 seconds calculation is correct. I'm still thinking how to get to the right answer on that.

 

[JonathanM]

As seems to be the growing theme, there's no obvious option to do that on the Ideal's. Unless I need to open it up and flick some kind of switch somewhere... at which point I need a GasSafe engineer as the front panel is head-to-toe room seal.

When I’ve thought about it a bit more, I don’t think the calculation I did above can be correct.

As regards the pump speed, I suggested that because it’s the only thing you seem to be able to change on the boiler. I really have no idea of whether it will do any good.

I think Johntheo5 will be right, in that it’s all about getting the return temperature down. If I sent you the right manual, then on page 39 it shows you how to take a reading of the return temperature from the boiler menu. Or you can measure the pipes directly with suitable thermometers.

I’m pretty sure that previously people have said that to get the return temperature down you’re supposed to balance the radiators and use the lowest pump speed possible. But this is beyond my practical experience. And then when you factor in TRVs and which zones to use, then that is well beyond my brain power!

Another poster had the Ideal Vogue, which I'm sure has the same pump, and was getting a 15C degree gap between flow and return at 50C flow temperature. But they had done the balancing. I don't know what the gap was before the balancing, or indeed if any measurement was actually taken beforehand. Also, don't know how big the house was or insulation.

 

[Johntheo5]

Can you post a link to that manual please.

 

[karlbbb]

Can you post a link to that manual please.

https://idealheating.com/uploads/do...tallation-Servicing-Guide-222362-1_lowres.pdf It was this manual. However, this is for the "Logic Max" and I have just a standard "Logic", so the manual doesn't cover my model.

I think I'm completely SOL when it comes to my system right now. The boiler is just too big and has no ability to change parameters to try and make a better situation. Shame, because I imagine a lot of people on this estate, and probably many others, are blissfully unaware they have an oversized boiler.

 

[Johntheo5]

JonathanM may have a link to your model. (OK, I see, as you say, its the link you showed, above)
I think I've asked before, how long roughly does it take the boiler to fall the 10C between burner off and burner on?.

 

[karlbbb]

JonathanM may have a link to your model. (OK, I see, as you say, its the link you showed, above)
I think I've asked before, how long roughly does it take the boiler to fall the 10C between burner off and burner on?.

I, stupidly, didn't take a note of that when I was watching burn times. I'll have a look next time the heating comes on.

 

[JonathanM]

JonathanM may have a link to your model. (OK, I see, as you say, its the link you showed, above)
I think I've asked before, how long roughly does it take the boiler to fall the 10C between burner off and burner on?.

Apols. I think the original link from karlbbb was to the Logic Max. I thought it was a bit weird for Persimmon to use the Max version! Here is the manual for the standard Logic, but this manual is from 2019.

https://idealheating.com/uploads/documents/Logic-Combi-Installation-Servicing-222351-1_inst.pdf

EDIT: It looks like there have been a couple of Logic models over the years. But this is the one called C35, so it looks right. If it works the same as this one, you can set the pump speed to 100% on page 38 in the section "Accessing the Installer Mode".

EDIT 2: In a Youtube review in 2017, it looks just the same.

 

[Johntheo5]

I, stupidly, didn't take a note of that when I was watching burn times. I'll have a look next time the heating comes on.

That's fine but maybe you (we) should stand back a bit and say, so what if the boiler cycles alot?, if its giving you the required room temperature?, cycling in itself doesn't lead to huge in efficiencies, probably ~ 3% or less.
Remember Evohome cycles the boiler continuously once the room temperatures are within something like 1C of the stat setting, don't know if your stat in TPI mode does likewise.?
I would certainly increase the pump speed to 100% after first taking a few readings while cycling at its default setting of 70%, you may finally settle for some intermediate setting.

 

[karlbbb]

Apols. I think the original link from karlbbb was to the Logic Max. I thought it was a bit weird for Persimmon to use the Max version! Here is the manual for the standard Logic, but this manual is from 2019.

https://idealheating.com/uploads/documents/Logic-Combi-Installation-Servicing-222351-1_inst.pdf

EDIT: It looks like there have been a couple of Logic models over the years. But this is the one called C35, so it looks right. If it works the same as this one, you can set the pump speed to 100% on page 38 in the section "Accessing the Installer Mode".

EDIT 2: In a Youtube review in 2017, it looks just the same. View attachment 283644

Ah thanks for that - I had indeed read that section but clearly hadn't twigged the pump setting was a permanent one; I'd falsely equated it with the other "tests".

Any potential downsides to running the CH pump at 100% all the time, other than increased wear and increased electricity use?

 

[karlbbb]

That's fine but maybe you (we) should stand back a bit and say, so what if the boiler cycles alot?, if its giving you the required room temperature?, cycling in itself doesn't lead to huge in efficiencies, probably ~ 3% or less.
Remember Evohome cycles the boiler continuously once the room temperatures are within something like 1C of the stat setting, don't know if your stat in TPI mode does likewise.?
I would certainly increase the pump speed to 100% after first taking a few readings while cycling at its default setting of 70%, you may finally settle for some intermediate setting.

My thermostats (ESi ESRTP4) are TPI-capable, but I haven't enabled the setting. The fact the house isn't suffering from huge temperature swings and me having manually lowered the flow temperature has meant the thermostats click off at around SP+0.5C reasonably comfortably right now.

If I've read the manual section screenshotted above, it looks like I only have a choice of 70% or 100%, with no middle ground available.

 

[vulcancontinental]

The Logic Max has a ten year warranty. Do you know if that is still in operation?

Ideals sold to developers have a 2 year warranty mostly.

 

[Johntheo5]

If the burner is only staying

My thermostats (ESi ESRTP4) are TPI-capable, but I haven't enabled the setting. The fact the house isn't suffering from huge temperature swings and me having manually lowered the flow temperature has meant the thermostats click off at around SP+0.5C reasonably comfortably right now.

If I've read the manual section screenshotted above, it looks like I only have a choice of 70% or 100%, with no middle ground available.

If the boiler is only running for say 19 secs or so for a number of cycles before finally running for a few minutes then increasing the pump speed to 100% may get it to not require these very short runs but run for a few minutes or so which is normal.

 

[JonathanM]

Any potential downsides to running the CH pump at 100% all the time, other than increased wear and increased electricity use?

I definitely think you should wait for a reply from somebody who knows this stuff. I'm pretty sure it's a 7m head pump, which I think means it's pretty powerful when run at 100%. It says 15-70 on it, and I've seen it referred to elsewhere as a 7m pump. By default, on your boiler, it runs at a variable speed between 70% & 100%.

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