Replacement Boiler - Which Make/Model?

[Kev.H]

After living in our current house for 21 years and with the original boiler past 25 years old, it is looking like we need to consider a replacement early next year. The boiler (Myson Apollo 30i) is noisy and we were lucky to get a particular spare part earlier last year. I always said that I’d keep it going until it died but I’d rather be in a position to make a considered change of boiler rather than having to choose in an emergency. It is serviced annually. I did spend 20 mins on the phone with the service co after the last service discussing a replacement but gave up when they said a new boiler would start from 3k even after their “contribution” of £500. I’d rather use a local installer (Milton Keynes) to fit it.

We use gas only for heating/hot water via this boiler. Annual gas use is approx. 20kW/h.

The house is a 4 bed detached with a loft conversion. At the time we did the conversion we converted to a pressurised system with a 250l megaflow cylinder. 3 bathrooms, 3 occupied bedrooms and 16 radiators. Boiler is wall mounted in the kitchen utility area on an external wall.

As always the difficult decision is what make and model to go for – or to rule out. Going on two of the boiler manufacturer’s sites comes back with recommendations of WB Greenstar 30i or Style 35kW, or Viessmann Vitodens 200-W.


I’d welcome any suggestions or tales of lessons hard learnt.

Thanks - Kevin

 

[muggles]

Ignore the boiler manufacturers' sites, they have no idea how to size a boiler correctly. If your current boiler is a Myson Apollo 30i, then its output is a maximum of 8.8kW. You absolutely definitely do not need a 35kW boiler to heat a house which is being heated perfectly well with 8.8kW (assuming it is, of course). A 35kW boiler will just cost a lot to run and be inefficient.

Based on the current boiler alone, I'd recommend a Viessmann 200-W 11kW, but it would be worth getting a proper heat loss calculation done to see what's actually needed.

 

[Razor900]

11kW sounds a bit mean for 16 rads and a UV. The current one could be a 30/50i which was around 15kW

If it's in the utility room it should be a reasonably straight forward swap especially if the programmer is also located there?

Condensate and pump overrun are the two usual pitfalls of this kind of job and it sounds as if they won't be an issue

 

[Kev.H]

Apologies to Andrew and Razor900. I've assumed it was a 30Si but I've removed the lower cover to find it is a 50Si which the owner's guide says delivers between 11.7 and 14.7Kw.

The programmer is in the same area as the boiler. The performance of the system, even after adding the extra load from the loft conversion has been quite acceptable with radiators heating quickly (as I've added/replaced radiators I've added TRVs) and the HW cyclinder re-heats quickly.

Getting condensate into a drain not too much of a challenge. Will need to drop down the wall under the boiler, through and under a worktop along a run of 1.5m to get to the washing machine waste. There are no outside drains.

 

[Razor900]

Did the system get sealed as part of the loft conversion? If so you will have a pressure gauge and an expansion vessel somewhere?

It just helps to decide what type of boiler you need.

 

[vulcancontinental]

I think there were a few 000's left off of the annual consumption figure, the average being between around 15000kWhrs.

If you were not cold and had sufficient hot water over the past coldest periods you know the current output will suffice. With a condensing boiler changing the configuration to priority domestic hot water either via onboard boiler controls or external boiler controls is something to consider to achieve better efficiency with a modulating control to align heating flow temperature with current load squeezes a little more from the system.

If the rads were sized by the developer they'll be tightly specced so modulated flow may slow heat-up times and you'd need to adjust them plus if you like radiators hot go for ali, if the house is occupied most of the time and you go for modulated flow go stainless.

I'm not transfixed in the spotlight of the current trend for excessive modulation to reduce cycling, as long as the lowest boiler output is no more than twice the lowest heat input the property would require during the heating season the efficiency losses are minimal and extended warranty of the boiler takes care of any wear and tear on components.

Just a purely personal opinion.

 

[Kev.H]

I think there were a few 000's left off of the annual consumption figure, the average being between around 15000kWhrs.

You're right, 20MW/h (20,000KWh)! I did think after I had posted it that my original figure was rather low!

 

[Kev.H]

Did the system get sealed as part of the loft conversion? If so you will have a pressure gauge and an expansion vessel somewhere?

It just helps to decide what type of boiler you need.

It did. Expansion vessel and pressure gauge/filling loop in the same airing cupboard as the HW tank

 

[Mottie]

You could get an 18KW to be on the safe side. My Vaillant ecotec plus 418 can be adjusted down to about 8kw max output and the price difference from a 15kw isn’t much.