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Discuss Which Worcester Bosch Boiler For Our Home? Please Help! in the Central Heating Forum area at

  1. Bazzy

    Bazzy Member

    Hi All,

    We may need to replace our boiler - the OLDER version Worcester Bosch 35Cdi (see images attached)

    1. Our home is a 1920's Semi
    2. 5 Bedrooms
    3. 2 Bathrooms
    4. 5 x Large (1800mm) Double Panel Radiators
    5. 1 x Large (1800mm) Single Panel Radiator
    6. 3 x Medium (1400mm) Double Panel Radiators
    7. 2 x Short Height Double Panel 1400mm Radiators
    8. 3 x Bathroom Towel Radiators
    We had a WB Engineer come round to try & fix the boiler but said parts were no longer available & recommended that we upgrade to the 42Cdi - he said this model will allow use to run as many hot water devices as we wish without one area losing out over another.

    After he left, the boiler started leaking again so another WB Engineer came round & he was strongly recommending the 29Cdi Classic (insisted that we choose the Classic version).

    Both are highly trained WB Professionals who know their stuff but I am a bit confused as to which one to believe since they both recommended two very different models so am wondering if anyone here can really help me out on which from the WB range is really best for our home?

    I was surprised that the 2nd Engineer strongly recommended a much smaller capacity model than the one we currently have as from what little I know, is that one has to either maintain the size you have to ensure good performance or go for as bigger/next model up to allow fro extra headroom so the boiler does not have to work as hard? I may be totally wrong on this as I am a novice hence coming here for advice.

    The 1st Engineer may have recommended the 42CDi as he believed that would service the size of our home best & the 2nd one might have recommended the 29Cdi instead as it has been over 15 years since we have had our current boiler & advances in boiler technology in this time might mean that these days a smaller capacity boiler may well be able to do the same job as a bigger one from yester-year - I do not know but I do believe Engineers were being sincere with their advice.

    Please can anyone recommend ANY Combi Boiler from the WB Range that would best suit our needs? I do not know how boiler size & capacity affects things like energy use & how it affects bills - I do not want a small boiler that takes longer to do things & hence uses more energy meaning more running & energy costs but am worried that the same might then also apply to getting a much bigger one - i.e. - it uses more energy than actually needed, hence higher costs etc?

    Flow rate is important since we have two bathrooms - my kitchen tap delivers about 17L/min & the 29Cdi delivers about 11L/min & the 42Cdi 16L/min if that has any bearing?

    Finally, I read somewhere that if one has two bathrooms and/or a bigger property, instead of a Combi Boiler, one should also consider a System Boiler? I have no idea what the latter is & not being technical, get somewhat bemused by all this so can anyone explain what they are & if they might be a better option for us?

    Would really welcome & be exceptionally grateful for any help/advice on which WB Boiler is best for our home!

    Many Kind Thanks,

    DSC04591.JPG DSC04594.JPG
  2. SimonG

    SimonG Trusted Plumber

    System boiler and unvented cylinder if water pressures and flow allow.

    oh and not a Worcester botch.
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  3. Bazzy

    Bazzy Member

    Hi SimonG,

    I will have to look into exactly what System Boiler & Unvented Cylinder is - how does it differ from a Combi Boiler may I ask? Is it all in one unit like a Combi or does it have lots of separate bits etc? Will there be lots of extra pipe work needed & will anything be have to be placed in the loft etc? It will be very difficult indeed for us to run new pipes etc from say the loft to elsewhere in the house.

    What sort of water pressures & flow are required then for this option please?

    May I ask why not a Worcester Bosch? I really know nothing about boilers but the reason the owner of the house wants to stick with WB is that when ever things have gone wrong with the current boiler, WB have been really great in getting it sorted - they can arrive usually within a day or so, usually always sort out the problems & their engineers have always acted very professionally regardless of who over all these years. It is this peace of mind that the owner really values with WB - they are round very quickly & always sort the problems out.

    Do any other brands offer the same/similar? We usually have some sort of Boiler Servicing Contract.

    Are there issues with WB that I must obviously be unaware of then that you good folks in the trade know about?

    What brands & models would you recommend then for our home please?

    Many Thanks,
    Last edited: Dec 10, 2018
  4. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Combi boilers are not designed to run multiple outlets. A system boiler and invented would give you best results at multiple outlets. Service contracts are pointless in my humble opinion most decent manufacturers offer a decent warranty these days on the proviso that that an annual service is carried out. Employ a local independent engineer to fit it and maintain it for you. Worcester are not what they were. For my money Vaillant/Glowworm
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  5. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Viessmann 222 at a min
    • Informative Informative x 1
  6. gmartine

    gmartine GSR

    How did you find your old boilers performance when running two bathrooms?
  7. Bazzy

    Bazzy Member

    Hi gmartine,

    I cannot say for certain with two bathrooms running but on the whole it was not too bad really - there were lots of times when someone would be having a shower & either the washing machine, Dishwasher and/or other hot water taps were in use at the same time & although there was a flow drop, it was just about acceptable for the short times the other hot water taps etc were on.

    Hope that helps!
  8. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Don’t do combi you’d be so much happier with unvented
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  9. Bazzy

    Bazzy Member

    Hi Riley,

    Can you please kindly give me some suitable examples of this unvented system so I can have a look & learn from - I am totally clueless about these things & have no idea what to look for & what might be any good.

    Many Thanks,
  10. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    It’s a boiler and hot water cylinder set up but at a good pressure and flow rate as long as incoming mains allows
    • Informative Informative x 1
  11. Bazzy

    Bazzy Member

    Hi Riley,

    Thanks for that - so there is a boiler part which hangs on the wall like the 35Cdi we have & a separate tank cylinder which stores hot water?

    Where is the cylinder installed may I ask? Next to the boiler or in the loft?

    All I know is our kitchen cold water tap produces about 17L/Min - is that good enough pressure & flow rate?

    Do you know how much these systems would cost & is this unvented type the same as a "System Boiler"?

    One of the WB Engineers informed me about one of their floor-standing boilers with a hot water tank - I think it was a 440 or 550 model - is that the same thing as this unvented system or system boiler?

    Many Thanks,
  12. Watermargin

    Watermargin New Member

    Hi i have a fully functioning 35cdi cw flue if your interested. Reason i kept it back was because it is a great boiler. Twin pumps and all that.
  13. Bazzy

    Bazzy Member


    Is it new or used may I ask? Is there any warranty on it & where in the UK are you please?

    I am doing my best to research boilers/options at the moment but for me, it is proving to be very daunting as I am just not knowledgeable enough about the various differences in brands & stuff that those in the trade might know.

    I know a few here have suggested an unvented system boiler with a separate tank but I really doubt that my home has/meets the absolute minimum required parameters to consider a unvented system boiler - I saw a video where someone in the trade stated that the absolute minimum incoming water flow must be at least 20L/mim but preferably much higher - mine is only 17L/min with the crude timed test I did. I have no idea what the water pressure is to my home but will try & get someone to check it for me - the person on the video said it must be an absolute minimum of 1.5 bar.

    If my place is unsuitable for these system boilers with a tank, then I am assuming my only option is to be stuck with a Combi?

    Many Thanks,
  14. Watermargin

    Watermargin New Member

    Hi again mine is old but you could easily swap out your existing no pipework change as is exactly the same. If you are investing in new system then i like and am biased towards worcester. I would of thought a 35cdi classic system boiler with a unvented cylinder would be great would gibe you mains pressure hot water however this is a lot of parts and install could cost well over 5000. Combis great but not brilliant when you have multiple bathrooms as flow is 16l a minute at best.
  15. Bazzy

    Bazzy Member


    Whereabouts are you please & how much for the boiler? Any warranty left on it that is transferable?

    I assume your a Gas Safe Registered Plumber & that it has been fully serviced in the time that you have had it?

    How much would it cost to have the old one removed & yours put in? I am assuming it is the newer model of 35Cdi & not the older version like mine?

    Many Thanks,
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