Seeking a boiler with a low(er) minimum modulation rate

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MJN

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We've currently got an Icos HE15 heat only boiler on an sealed system (and UVC with 19kW coil) and whilst it works well enough it is 13 years old now and so I've been thinking about what I might eventually replace it with when/before the time comes. The system is well balanced with an average 11°C drop across the radiators as recommended by the MIs but I am finding it is having to cycle a fair bit and have put this down to it not being able to modulate down low enough for the heat demand of the house (2007 build so reasonably well insulated). We've got around 9500W of radiator output @ DeltaT of 50 but we run closer to to a DeltaT of 40 so it is probably more like 7500W. The specs say the boiler has an output range of 8.8 - 14.7 kW.

I am wondering if anyone can point me towards system or heat-only boilers that have a (much?) lower minimum output rating? I would like to run at lower flow temperatures too so presumably a low minimum output rating would help in that respect? Ideally it'd give good support for Opentherm control too, just to add an extra complication to the ask.

I've seen the Intergas HREOV18 which has a range of 6.1 - 18.2 KW and the Ideal Logic+ Heat H15 which has a range of 4.8 - 15.0 kW so both offer improvements in the minimum modulation respect, and it sounds like they both support Opentherm well? Perhaps they are low enough to not need to look any further but I thought I'd throw it out to those in the know for comments/advice?
 
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The Intergas HREOV18 is an open vent boiler you probably need the HRESB18, personally I would go for the intergas but there are others
 
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muggles said:
The Viessmann 200-W goes down to 1.9kW
Click to expand...

Wow, that's like a candle! ;) Thanks, will take a look.

ianmcd said:
The Intergas HREOV18 is an open vent boiler you probably need the HRESB18, personally I would go for the intergas but there are others
Click to expand...

I'd been led to believe (not sure where now to be honest; certainly not the MIs as they seem particularly light in detail on a variety of subjects) that the HREVOV18 can be used on a sealed system too. I'll check out the HRESB18 though, and thanks for the vote of preference (at least between the two) as they all sound equally great in the glossy brochures hence some level of personal recommendation is helpful.
 
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MJN said:
I'd been led to believe (not sure where now to be honest; certainly not the MIs as they seem particularly light in detail on a variety of subjects) that the HREVOV18 can be used on a sealed system too.
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It may be able to be altered to be used on a sealed system, why buy a boiler that needs to be altered when you can get one out of the box already set up for a sealed system , when the SB is cheaper
 
ianmcd said:
It may be able to be altered to be used on a sealed system, why buy a boiler that needs to be altered when you can get one out of the box already set up for a sealed system , when the SB is cheaper
Click to expand...
Can't argue with that logic, and it's making me wonder what led me down the path to the OV18 in the first place now. Thanks!
 
Just reading the MIs for the SB18 and it says:

MIs said:
8.1.2 Thermostatic radiator valves

If all radiators are equipped with thermostatic or radiator valves, an auto bypass must be fitted in order to guarantee minimum water circulation. The auto bypass must be at a distance of at least 20 ft from the appliance in order to prevent overheating of the appliance. A radiator without thermostatic valves is not a suitable by-pass.
Click to expand...

That sounds somewhat contradictory to me? The first sentence implies that if *not* all radiators are fitted with TRVs then you don't need a bypass (which would make sense to me - there'd always be a water pathway available). But then the last sentence undermines this by saying a radiator with a TRV is not suitable bypass. In what circumstances would you therefore not need a bypass? The difference in spelling of bypass/by-pass makes me wonder if they sentences might've been written by different people at different times i.e. the latter was added at a later date, perhaps given a recognised risk of someone manually closing off the non-TRV radiator(s) without realising they needed to stay open?
 
MJN said:
Can't argue with that logic, and it's making me wonder what led me down the path to the OV18 in the first place now. Thanks!
Click to expand...

Maybe you wanted an Open Vent because you didn't want to pressurise your system (which, maybe/presumably is already un-pressurised?) That might have been because the system is older but doesn't have any existing leaks and you didn't want to risk pressurising it to 1.5 or even 2 bars and risk opening up a can of worms?
Maybe you wanted to stick with the ease of access (and replacement) of the current circulation pump, as opposed to it being within the boiler?
Maybe you thought the absence of an expansion vessel within the boiler was one less cause of concern?

But, conversely, a new System Boiler with, perhaps a 10 year warranty, would have the boiler, the pump and the expansion vessel all covered by warranty (provided you'd paid the £70 or £80 a year to have it serviced, of course .... and which we all do anyway, don't we?) and you wouldn't have a Feed and Expansion tank in the loft - along with it's pros and cons.

Maybe you consider a sealed/pressurised system to be more "efficient" (I often read that that it, apparently, is) and less prone to corrosion given that there's no (or far less) exposure to open air, as there is with an OV?

Maybe you fancied a stainless steel heat exchanger. There seem to be very few Open Vent boilers with SS HX's but much more choice if you had a sealed system - I believe Viessmann do a S/Steel HX in an OV boiler.

All pretty straightforward then :)
 
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Mr.B said:
Maybe you wanted an Open Vent because you didn't want to pressurise your system (which, maybe/presumably is already un-pressurised?) That might have been because the system is older but doesn't have any existing leaks and you didn't want to risk pressurising it to 1.5 or even 2 bars and risk opening up a can of worms?
Maybe you wanted to stick with the ease of access (and replacement) of the current circulation pump, as opposed to it being within the boiler?
Maybe you thought the absence of an expansion vessel within the boiler was one less cause of concern?

But, conversely, a new System Boiler with, perhaps a 10 year warranty, would have the boiler, the pump and the expansion vessel all covered by warranty (provided you'd paid the £70 or £80 a year to have it serviced, of course .... and which we all do anyway, don't we?) and you wouldn't have a Feed and Expansion tank in the loft - along with it's pros and cons.

Maybe you consider a sealed/pressurised system to be more "efficient" (I often read that that it, apparently, is) and less prone to corrosion given that there's no (or far less) exposure to open air, as there is with an OV?

Maybe you fancied a stainless steel heat exchanger. There seem to be very few Open Vent boilers with SS HX's but much more choice if you had a sealed system - I believe Viessmann do a S/Steel HX in an OV boiler.

All pretty straightforward then :)
Click to expand...

MJN said:
We've currently got an Icos HE15 heat only boiler on an sealed system
Click to expand...


Someone not reading the whole post :rolleyes:
 
The intergas xclusive goes down to 4kw, it can be setup to be a system boiler.

It also works very well with opentherm, which the veisman does not.

The Atag boiler is another option and goes to 4.5kw and is also very good with opentherm.
 
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Mr.B said:
Guilty as charged.

It's time I stopped posting.
Click to expand...

:D No problem at all... I appreciate the efforts anyway! I suspect I was just thinking about a like-for-like replacement for the Icos i.e. heat only, external pump, simple as possible etc.
 
ianmcd said:
It was you that wanted recommendations for system boilers
Click to expand...

Yes, I was just saying that what originally led me to the OV18 was probably a search for heat only boilers but I have since broadened my scope to include system boilers too. I can see pros and cons with both.
 
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