Boiler advice

Armstrong86

I’m in the process of getting a new combi boiler and the 2 I got recommended from the plumber were the Worcester Bosch 28cdi Compact (I asked for a Worcester price) and his recommendation, the Baxi Platinum 28erp. I live in a 3 bedroom new build (2009) and have one shower/bath that runs off the boiler and 9 radiators.

I’ve always thought I’d get a Worcester but after looking at the Baxi user reviews I’m kinda split now. There’s not much between them except I think one is 24kw and the other is 28kw but I’ve struggled to find an answer to what exactly that means. Is that for the output of litres/min for hot water?

Any advice on which one to go for is much appreciated.

Brummie85

Why do you need a new boiler in a property that is still relatively young? Have you checked to see if you are still under any warranty.

The KW rating describes the capacity of the boiler to provide energy in the form of heat. KW is a measure of power and can be applied to various types of system, including heating/cooling, mechanical systems and electricity.

On larger properties with demand to supply more then 1 bathroom, boilers with larger KW ratings are the norm. Probably 32 KW upwards.

The other deciding factor is how your home retains heat. For your modern 3 bed, 1 bathroom house that should be well insulated and energy efficient, a 24 KW boiler should be more then sufficient.

For properties that have non cavity walls, lack of insulation, single glazing etc these are all horrible in terms of their u values and will increase the overall size of boiler required to compensate for the heat that escapes.

But before you go for a new boiler. See what's up with the one you have and if it's worth repairing instead.

Incidentally, I have myself just bought a new boiler today. It's by a lesser known brand called Intergas. But they are a top 5 according to Which?. Their design makes them reliable due to less parts and they will still supply hot water even if the diverter valve fails (they don't need this valve as other combo boilers do, so therefore it can't fail). I've only gone for the cheaper Rapid model, because I'll be moving in 2 or 3 years. It's still a very good boiler, but misses some features I don't need on their pricier models.

Look them up. They are worth considering.

Armstrong86

The house was fitted with an Ideal Isar and it's had numerous breakdowns and repairs plus the fact it’s just so damn noisy. With a baby due in October I don’t want another breakdown in winter. Two of my neighbours that had the same boiler have needed to have them replaced in the past year. I suppose my thinking is the money is there so I’m just getting it done.

Thanks for the advice and explaining the KW to insulation, makes a lot of sense now.

Brummie85

Armstrong86 wrote: »

Is that for the output of litres/min for hot water?

Only just spotted this part of your question. It changes my advice.

Yes. With combi boilers this is mostly linked to your main water pressure. The faster the flow of your cold mains, the harder your boiler will need to work and with that a higher output value is required.

The hot water flow information is specified separately though. It's called DHW flow rate, often quoted at two different tempratures for change of water temp. The hotter the water you ask for, the slower the flow. But if you look at the same range of boilers with different KW outputs, you'll notice that the higher KW models will manage better flow rates at the same temperatures.

Although a 24KW boiler is rated adeqautely for smaller properties with up to 10 rads and 1 bathroom, it doesn't give a great output for hot water. Going up to 28KW would be a decent idea. You will get a better DHW flow, but it will also allow you to add another couple of rads, or fit larger rads in some rooms instead if you desire. a 24KW boiler was all the builders needed to put in to cover the heating, so it's all they would do. It's the bare minimum to cover the requirements.

As for the boilers you mentioned, at 28 KW their quoted flow rate is identical at 11.5 litres/min for a 35 degree rise in temp. There's next to nothing in it on other performance criteria such as energy efficiency. You could pick either and not think the other is significantly better or worse. If the warranty is significantly better on the more expensive Worcester and the overall price difference from the installer isn't crazy - that may have been the deciding factor for me in your situation.

Congratulations on the baby on the way !

Armstrong86

Thanks again.

After looking at them more in detail both boilers are 24kw for CH and 28kw for DHW. It’s about £150 more all in for the Worcester than the Baxi but the Baxi does have a longer warranty.

My head’s pickled the past few days looking at boilers! I suppose when I’m spending a lot of money I just want to make sure I get it right. My dad had a Worcester Combi fitted about 7 years ago and has only had one problem with it and the after service he got to repair it was fast and efficient. It also runs so quietly.

I’ll mention Intergas to my plumber and also look at them online.