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Discuss Boiler swap. INTEC 40GS to Worcester Greenstar 32CDi Compact Combi in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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Dear Forum members,

Hope that you are all doing well!
  • We are thinking of moving our existing boiler from its cupboard to a bathroom corner to free up some space
  • A local specialist has recommended that we install a smaller boiler, so that it fits into the bathroom nicely
My goal is to ensure that the proposed replacement (Worcester Greenstar 32CDi Compact Combi) will perform adequately when replacing the existing boiler (INTEC 40GS), which is 5 years old, had a diverter valve replacement, and is on warranty (annual plan).

House
Semi-detached, new-build (I would say - well insulated), 2-bedroom, two-story
9 radiators, two showers and a bath

Boiler comparison

Range:Greenstar CDi CompactInTec
Brand:Worcester BoschAlpha
Flow Rate:11 L/min18.4 L/min @ 30°C, 15.8 L/min @ 35°C
KW:3240
Model Number:32CDi LPG40GS
Rated Heat Output (Prated or Psup):24 (Prated)28
Water Heating Energy Efficiency %:89.890
Water Heating Declared Load Profile:XLXL
Seasonal Space Heating Energy Efficiency %:94, A/94%92
Water Heating Energy Efficiency Class:AAlpha
Sound Power Level (Indoors):52
Seasonal Space Heating Energy Efficiency Class:AAlpha
Depth (mm):280360

Could we get away with the new CDi Compact? Or should we stick with the objectively more powerful 40GS?
I would be very grateful if you could share your experience!

Thank you in advance!
 
I think you will struggle to find someone prepared to move your existing boiler.
I’m not a fan of Worcester but is the 36kw version an option?
 
I don't think the flow rate you quote for the WB 32CDi is correct, I had a quick look at a couple of sources that state it should be 13.1 l/m and the 36 CDi is around 15 l/m.

As Scott suggests I don't know why the company are quoting for the less powerful WB boiler as they are the same physical size except to keep the price down. You already have a really good flow rate (if you get it) you'll miss it but as you say maintaining performance is key.

If you haven't done it, it's a crude method but just measure how long it currently takes to fill a 1 litre container and do the maths and see what the true HW flow rate is before you go chasing it. As it's a new build chances are you have the requisite water and gas pressure and flow rates that allow your current boiler to work at it's optimum but that isn't always the case.

My instinct is to say that will be quite an outlay for a bit more cupboard space and replace a perfectly reliable boiler so have you exhausted all your options in that regard? Without meaning to be condesending perhaps an innovative chipie could redesign or incorporate same additional or hidden cupboard space somewhere.
 
The heating would be ok but you will struggle with the hot water delivery showers need a minimum of 8 litres a minute for a decent shower, even if your fit flow restrictors you will struggle to run two hot water outlets at the same time. Kop
 
Duh more coffee required, well spotted I didn't see that two showers were in use and obviously that's why such powerful boiler was put in. Easy decision for me then, keep your current system and find some space elsewhere.
 
I think you will struggle to find someone prepared to move your existing boiler.
I’m not a fan of Worcester but is the 36kw version an option?
Hi Scott,

I think the 32 kW option was suggested because of its size:
1635148478149.png

It would fit into a 30cm cupboard.
 
I don't think the flow rate you quote for the WB 32CDi is correct, I had a quick look at a couple of sources that state it should be 13.1 l/m and the 36 CDi is around 15 l/m.
Thank you for highlighting this. I took the values from here Worcester Bosch Greenstar CDi Compact 32CDi NG combi boiler | Wolseley - https://www.wolseley.co.uk/product/worcester-greenstar-32cdi-combi-boiler-only/ but it must be wrong. I wish I could edit my original post to correct the mistake.

As Scott suggests I don't know why the company are quoting for the less powerful WB boiler as they are the same physical size except to keep the price down. You already have a really good flow rate (if you get it) you'll miss it but as you say maintaining performance is key.
I think they are quoting for it because of the space. Please see my response to Scott above. We are trying to free up the space to install an additional set of stairs into the loft and have some unused space in the bathroom.

If you haven't done it, it's a crude method but just measure how long it currently takes to fill a 1 litre container and do the maths and see what the true HW flow rate is before you go chasing it. As it's a new build chances are you have the requisite water and gas pressure and flow rates that allow your current boiler to work at it's optimum but that isn't always the case.

I see! So the actual flow rates can be less than what the current boiler could deliver.. I will check that, thank you!

My instinct is to say that will be quite an outlay for a bit more cupboard space and replace a perfectly reliable boiler so have you exhausted all your options in that regard? Without meaning to be condesending perhaps an innovative chipie could redesign or incorporate same additional or hidden cupboard space somewhere.

It is a great idea and I now see why it is not a great idea to touch an existing boiler.. The boiler move is to free up space for that set of stairs to the loft, but perhaps the chippie could design an appropriate set of stairs! Will investigate. Thanks again!
 
The heating would be ok but you will struggle with the hot water delivery showers need a minimum of 8 litres a minute for a decent shower, even if your fit flow restrictors you will struggle to run two hot water outlets at the same time. Kop
This is very useful information, thank you!
 
Two things, as you've discovered the external size (casing) for the compact CDi range is the same whatever the power rating of the boiler.

The flowrate you listed from WB is l/m @ 40 degrees whereas the max flowrate from your Alpha you highlight is l/m @ 30 & 35 degrees C. Easy mistake to make so to compare like for like, find or phone WB for the 36CDi data sheet and get the numbers for l/m @ 30 & 35 degrees C for a fair comparison.
 
I think they are quoting for it because of the space. Please see my response to Scott above. We are trying to free up the space to install an additional set of stairs into the loft and have some unused space in the bathroom.
It would be a lot cheaper to put a cupboard in the bathroom to use the space than to move the boiler. One possibility I'd find attractive would be to create a drying cupboard with a dehumidifier, which could have its drain plumbed in.

Be careful about how you use the roof space in a new house. The joists are often 'engineered', i.e. won't take much additional load. Also, there'll be a lot of insulation that you can't compress down without problems.
 
Two things, as you've discovered the external size (casing) for the compact CDi range is the same whatever the power rating of the boiler.

The flowrate you listed from WB is l/m @ 40 degrees whereas the max flowrate from your Alpha you highlight is l/m @ 30 & 35 degrees C. Easy mistake to make so to compare like for like, find or phone WB for the 36CDi data sheet and get the numbers for l/m @ 30 & 35 degrees C for a fair comparison.

Excellent point! I did have to 'hunt' for the 35 degree value for the Worcester, but found it here
1635157147329.png


36CDi Compact - 14.7 @ 35°c ∆T
InTec 40 GS - 15.6 @ 35°c ∆T

This isn't such a big difference. I hope I can trust these numbers! :)
 
Do a HW flow test and see if it's true. :)
Bath tap
6 seconds - 1 litre = 10 litres per minute

and, while the bath tap keeps running:

Bath sink
6 seconds - 0.5 litres = 5 Litres per minute

I don't know what the maximum could be, but it definitely does 15 Litres per minute.
 
Was the basin tap running when you measured the bath?

Otherwise you could have had 10 at bath, but this dropped (to say 5) when you measured the basin at 5. - in which case you only have 10, not 15.

Just checking your method 😉
 
Was the basin tap running when you measured the bath?
Thank you for checking! Yes, I opened both initially, allowed the water to run for a few seconds to get hot, then proceeded to place the kettle under each facet ;)

What may have hindered the measurement is that I think that our sink tap has a flow restrictor/aerator and I couldn't get the maximum flow tested (with the sink being limited).
 
A viessmann100 would be my choice for you bin the worcester idea this boiler would future proof your property and can get a 10 year warranty if fitteded by a accredited installer H2 ready built in wifi really well thought out , and dont forget you can only get out what you can put in , as winter approaches water temperatures in the ground will drop and as a consequence your litres per minute will reduce for hot water . Kop
 

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You fitted many KoP? It's a touch deeper than the offered WB but I agree it's worth it. Didn't realise the HW flow rate was that good and I did the bliming course.
 
A viessmann100 would be my choice for you bin the worcester

Thank you for the suggestion! Apart from WiFi I don't yet see why it's a better choice.

It's as large as our existing InTec G40 and as powerful
There will be a 10-year warranty on the Worcester too, as I was told

As much as I like the appeal of the technology coming from the country highly dependant on gas (Germany), and therefore knowing a good boiler, I can't see how it's better at this stage
 
As much as I like the appeal of the technology coming from the country highly dependant on gas (Germany), and therefore knowing a good boiler, I can't see how it's better at this stage

Respectfully how would you know?

The Viessmann has...

Far better modulation 10:1 rather than 4:1 ish.
Stainless steel hex rather than aluminium
H2 ready
ViCare app
Wifi/interweb ready
Extendible warranty to 12 yr
Bolt on weather comp
More efficient
About the same price
 
Respectfully how would you know?

The Viessmann has...

Far better modulation 10:1 rather than 4:1 ish.
Stainless steel hex rather than aluminium
H2 ready
ViCare app
Wifi/interweb ready
Extendible warranty to 12 yr
Bolt on weather comp
More efficient
About the same price

I believe the new Worcester eg 8000 is 20-1 like the old 200 which surprised me
 
You fitted many KoP? It's a touch deeper than the offered WB but I agree it's worth it. Didn't realise the HW flow rate was that good and I did the bliming course.
Ive fitted 3 up to now and another one lined up and all worked faultlessly weather compensation is great for a well insulated home and will definitely cut the fuel costs in my view far better than a worcester.
 
Thank you for the suggestion! Apart from WiFi I don't yet see why it's a better choice.

It's as large as our existing InTec G40 and as powerful
There will be a 10-year warranty on the Worcester too, as I was told

As much as I like the appeal of the technology coming from the country highly dependant on gas (Germany), and therefore knowing a good boiler, I can't see how it's better at this stage
You asked for advice and we gave it if you choose to not take it then its your proactive i hope it all works out. Kop
 
Respectfully how would you know?

I wouldn't know! I meant that I haven't seen any 'pros' posted here. But you have provided some in your response. Thank you!

My point is that if someone had a fully functioning boiler covered by warranty, then they wouldn't upgrade solely based on the features you have provided.
But then again, maybe some people would. Thank you for the food for thought! I really appreciate you sharing the knowledge!
 
I wouldn't know! I meant that I haven't seen any 'pros' posted here. But you have provided some in your response. Thank you!

My point is that if someone had a fully functioning boiler covered by warranty, then they wouldn't upgrade solely based on the features you have provided.
But then again, maybe some people would. Thank you for the food for thought! I really appreciate you sharing the knowledge!

It didn't read like that but thanks for the clarification.

From memory I think the Viessman 100 is a fraction deeper (10cm?) than the WB compact 36CDi which is what you'd need for comparative performance of your existing boiler. As outlined above it is a far superior boiler for approximately the same cost so if you go for the boiler move to develop the stairs/loft I'd make room for it.
 
It didn't read like that but thanks for the clarification.

From memory I think the Viessman 100 is a fraction deeper (10cm?) than the WB compact 36CDi which is what you'd need for comparative performance of your existing boiler. As outlined above it is a far superior boiler for approximately the same cost so if you go for the boiler move to develop the stairs/loft I'd make room for it.
Fitting this one at the moment the new 100w 35 kw with built in wifi. Kop
 

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