Worcester Bosch RD537i - Heating Output and Suitable Alternative

tnarg999 · 2 May 2017

Hi,
Can anyone tell me which figure on the attached for my British Gas (WB) RD537i is the central heating output normally used in comparisons? I think it is 37.1KW @ net 80/60 deg.

This boiler is 13 years old and other than early day gas valve fault, it's been trouble free and I'm pleased with it.

The issue I have now is that I want to move this boiler into a new utility area to get it out of the kitchen - it's a bit of a beast, but this was largely due ( I think) to solve the low flow rate we have. The new location would mean venting close to a boundary and I therefore need a flume/plume kit to vent it up and angled. Unfortunately WB don't make a flume kit for this boiler, which I found surprising - aren't they all comparable?

So the upshot looks like I'll have to get a new boiler - Can anyone suggest a good replacement of similar performance? I've been recommended an Ideal Logic Plus, but only seems to be 24KW heating.

Thanks

Agile · 2 May 2017

It is a combi boiler and so the power is related to water heating and not central heating. You have been accustomed to 37 kW and so I would not recommend anything less than a 32 kW boiler.

Your gas registered installer will suggest suitable alternatives.

Worcester were very slow to start selling plume management kits which surprised me.

Unfortunately we are only allowed to use the manufacturer's flue components sold for the specific boiler.

I expect there may well be other flues with the kits which would fit but we are not permitted to use them!

Tony

tnarg999 · 2 May 2017

Let me rephrase the question - Will an Ideal Logics "Plus" C35 give the comparable CH output as the RD537i? I don't really understand how Combi's work but find some websites quote 24KW CH Output for this boiler and others 35KW..

https://www.plumbnation.co.uk/site/ideal-logic--35kw-combination-boiler-natural-gas-erp/

Would you or anyone else recommend this Ideal boiler?

thanks

muggles · 2 May 2017

As Tony has suggested, it's highly unlikely that your home needs 37kW of heat. I'd be surprised if it needs even half that. My 4-bedroom 1970s house uses 14kW. To size your replacement boiler, you need to know what your incoming mains flow rate is in litres per minute. You can find this out by timing how long it takes for a bucket of known capacity to be filled by your cold bath tap.

I'd recommend an Intergas ECO RF with 10 year warranty - similar price to the Logic and a much better boiler

D_Hailsham · 2 May 2017

tnarg999 said:
I don't really understand how Combi's work

This diagram may help (not all combi boiler work in exactly the same way, but the principal is the same).

When hot water is not required, the heated boiler water is pumped through the radiators.
When a hot tap is turned cold water from the mains starts flowing through the secondary heat exchanger.
A flow detector operates the diverter valve so the hot boiler water produced by the primary exchanger passes through the secondary exchanger.
The cold water is therefore heated up.
Because the cold water is travelling relatively fast a considerable amount of heat is required, depending on the flow rate.
For example:
Flow rate 10 litres/minute; temperature rise 35C (say 5C to 40C) will require a heat input of approx 25kW (a rise to 60C would need 38kW).

The central heating requirement is normally much lower -as others have said. You can find out how much your house needs by using Baxi Whole House Boiler Size Calculator.

tnarg999 · 2 May 2017

muggles said:
As Tony has suggested, it's highly unlikely that your home needs 37kW of heat. I'd be surprised if it needs even half that. My 4-bedroom 1970s house uses 14kW. To size your replacement boiler, you need to know what your incoming mains flow rate is in litres per minute. You can find this out by timing how long it takes for a bucket of known capacity to be filled by your cold bath tap.

I'd recommend an Intergas ECO RF with 10 year warranty - similar price to the Logic and a much better boiler

We have 15 litres per min at the Garden tap and 22 litres at the road meter (according to the water board) I think this is why we had a high output boiler as we need to run the tap/shower at full to make it worthwhile.

Razor900 · 2 May 2017

D_Hailsham said:
This diagram may help (not all combi boiler work in exactly the same way, but the principal is the same).

View attachment 118504

Blimey there's a lot of parts there to go wrong

Less is more

muggles · 2 May 2017

tnarg999 said:
We have 15 litres per min at the Garden tap and 22 litres at the road meter (according to the water board) I think this is why we had a high output boiler as we need to run the tap/shower at full to make it worthwhile.

An Intergas ECO RF 36 will do you nicely then

rules&rulers · 2 May 2017

13 years and just 1 part changed,if only WB sourced more boilers from Junkers and just re badge them.

Boiler heating output,well your installer can work that out on site.

tnarg999 · 4 May 2017

rules&rulers said:
13 years and just 1 part changed,if only WB sourced more boilers from Junkers and just re badge them.

Is this particular boiler a re-badged Junkers boiler then?

rules&rulers · 4 May 2017

Many of the early worcesters were just re badged junkers products,kind of a good idea.

D_Hailsham · 4 May 2017

Junkers is part of Bosch Thermotechnology, just like Worcester.

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Worcester Bosch RD537i - Heating Output and Suitable Alternative

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