Boiler options - Ideal, Worcester Bosch or Viessmann?

[vulcancontinental]

The curve ball you asked for

Vokera Unica Max 35 or 40. Range rate down to what the heat load is at present then increase it later when the extension is built.

The boiler control can also control a heat pump, solar thermal, solar photaic if you add bits later.

Stainless exchanger, 10 years warranty OpenTherm and weather comp ready, 1:8 modulation active combustion control.

Not cheap but not too dear either

 

[Nozzle]

Stick ATAG on your list of potentials.

Nozzle

 

[Gizmo1975]

Thanks for all the comments.

Intergas Xclusive is well worth looking at if you do go for a combi, and it's easily converted to a system boiler in future if you do upgrade to an unvented cylinder.

Decent modulation range and future-proof, but only 2 approved installers within 30km. Will look into this one further, thanks.

The curve ball you asked for Vokera Unica Max 35 or 40.

Definitely like the future-proofing aspect, but the modulation is a bit so-so. Will add it to the research list, thanks!

Stick ATAG on your list of potentials.

Thanks - the Economiser looks interesting (in comparison to the standard combi anyway) - will have a poke to see how its water heating energy efficiency of 94% (presumably its 'Built-in Passive Flue Gas Heat Recovery Device') compares to others I'm looking at. Don't all (recent) modulating boilers have bottom-up modulation, or is this specific to Atag?

 

[vulcancontinental]

A lot of people put store by modulation defacto and to an extent they're right but 3 things should be remembered.

As long as the burn time exceeds 3 minutes the efficiency loss is around 1.5% (10 second cycles it's 12%) £800/annum space heating bill = £8.

It's argued more cycles wear out the appliance which is possibly true but the older boilers cycled continuously for 20 years plus. Just choose a boiler with a decent warranty on the whole machine not highlighted components.

The human body does not notice changes in temperature up to 4°C as long as they're slow, 1°C/minute and there's no draught. So slow changes with anti cycle delays on the boiler when cycling (or a combi when supplying hot water) are not noticable.

 

[BlueLoo]

A lot of people put store by modulation defacto and to an extent they're right but 3 things should be remembered.

As long as the burn time exceeds 3 minutes the efficiency loss is around 1.5% (10 second cycles it's 12%) £800/annum space heating bill = £8.

It's argued more cycles wear out the appliance which is possibly true but the older boilers cycled continuously for 20 years plus. Just choose a boiler with a decent warranty on the whole machine not highlighted components.

The human body does not notice changes in temperature up to 4°C as long as they're slow, 1°C/minute and there's no draught. So slow changes with anti cycle delays on the boiler when cycling (or a combi when supplying hot water) are not noticable.

Do you have sauce for the above?

Very interesting. I'd like to do some reading on them.

 

[Harry Bloomfield]

It's argued more cycles wear out the appliance which is possibly true but the older boilers cycled continuously for 20 years plus. Just choose a boiler with a decent warranty on the whole machine not highlighted components.

However, older boilers were simpler, much less to wear and generally fewer components to wear, plus the parts were much cheaper.

The human body does not notice changes in temperature up to 4°C as long as they're slow, 1°C/minute and there's no draught. So slow changes with anti cycle delays on the boiler when cycling (or a combi when supplying hot water) are not noticable.

I would say the 4C has to be wrong, I notice a drop in temperature in the house of 1C.

 

[vulcancontinental]

To briefly answer points above, body sensing temp change was a Google search throwing up a research result, efficiency loss was the findings of independent research paper, I'll look for it later, older fan flued boilers were not solid state electronics but incorporated mechanical switching, solenoids and relays but around the same number of parts; fan, gas valve PCB, flow switch, pump. The bits I'd say there are more of now are temperature sensors, thermistors, simple and solid state. Definitely the boilers, except Vokera (ACC), with active combustion control do have more complication and bits and expensive bits at that. Those boilers are not mainstream however.

 

[vulcancontinental]

https://journals.sagepub.com/doi/full/10.1177/0143624420927352
https://assets.publishing.service.g...t_data/file/47962/1149-condensing-boilers.pdf
https://journals.sagepub.com/doi/full/10.1177/0143624418794552

 

[Harry Bloomfield]

To briefly answer points above, body sensing temp change was a Google search throwing up a research result, efficiency loss was the findings of independent research paper,

Temperature feel is very subjective I find, very dependent on what you are doing, what you have just done and what you are wearing. I have the over night set to 16C, changing to 18C at 10am - as measured in the hall. I find I am comfortable in the +16C, for the couple of so hours after rising, but then begin to feel a bit chilly at around 10am. By late afternoon/ evening I often manually nudge it up to 19/20C.

I'll look for it later, older fan flued boilers were not solid state electronics but incorporated mechanical switching, solenoids and relays but around the same number of parts; fan, gas valve PCB, flow switch, pump.

I was comparing my present boiler against our old faithful Glowworm of the 1980's. It just involved an always lit pilot light, gas valve, burner and thermocouple to prove the pilot light was lit and an output temperature thermostat. Other than cleaning of the burner, it only ever cost a couple of thermocouples, a peizo ignition spark electrode and a replacement gas valve when the solenoid went o/c. All cheap as chips.

 

[vulcancontinental]

Temperature feel is very subjective I find, very dependent on what you are doing, what you have just done and what you are wearing. I have the over night set to 16C, changing to 18C at 10am - as measured in the hall. I find I am comfortable in the +16C, for the couple of so hours after rising, but then begin to feel a bit chilly at around 10am. By late afternoon/ evening I often manually nudge it up to 19/20C.



I was comparing my present boiler against our old faithful Glowworm of the 1980's. It just involved an always lit pilot light, gas valve, burner and thermocouple to prove the pilot light was lit and an output temperature thermostat. Other than cleaning of the burner, it only ever cost a couple of thermocouples, a peizo ignition spark electrode and a replacement gas valve when the solenoid went o/c. All cheap as chips.

Yes, the temperature changes felt was as memory serves the example of a seated adult in good health.
I felt it only fair to compare standard efficiency boilers with a fan and no pilot according to book figures around 70% efficient and the Glow Worm you mention around 60%. When those boilers were in systems which were up to or approaching target temp and with no modulation they'd cycle and book figures became less relevant. I would say a £5 thermocouple was the most common failiure and the ignitor next. When young and enthusiastic starting out I calculated the pilot as costing £22/year (this was 30 years ago plus) when NG was far, far cheaper than it is now.

 

[CBW]

but only 2 approved installers within 30km. Will look into this one further, thanks.

Do they have to be approved installers for any of the boilers you’re asking about?

 

[muggles]

Intergas don't require you to be an approved installer, and I don't think Ideal do either. WB and Viessmann definitely want you to have gone on one of their sales days to be able to offer the extended warranty

 

[Madrab]

Yup, the warranty is the warranty as far as Intergas is concerned regardless of who fits it, doesn't need to be an accredited installer and all they look for is to use their filter to extend the stock warranty a further 2 years.

Of course it's a bit of a sales tactic and their filter is on the expensive side but it's a pretty solid bit of kit (rebadged Fernox Omega filter) and an extra 2 years warranty for something that would normally be fitted anyway is a bit of a no brainer IMO.

 

[JCK1]

I went for the viesmann 100-w combi in april 2021, 35 kW on hot water , I have heating range rated down to 12kW , it operates very well on opentherm (evohome control on all 11 zones in house) . Modulation turn down on heating is 3.2 kW . The boiler is in loft , the vicare app tells me system operating paramaters from my phone (flow temperature, modulation %, system pressure ) , the app now also gives gas used each day for heating and hot water . There are no rubber pipes , it is copper. so far all working very well , opentherm keeping boiler in condensing range most of time. I selected this boiler because a) Stainless Steel heat exchanger b) opentherm compatibility , the WB does not work well with the Opentherm even with the the adaptor c) lowest turn down to 3.2 kW that I could see on all the boilers (except Viessman 200-W but that one does not support opentherm)

 

[Gizmo1975]

Thanks for all the suggestions here. Due to a change in circumstances this has been put on hold for the time being, and am now back to the drawing board of combi vs unvented vs vented. To avoid the wrath of the experts here, I'll be doing more research into it, AND THEN I may come back with a question or two!

All the best