Update gravity central heating system to combi

Discussion in 'Plumbers' Talk' started by sbis, Nov 18, 2009.

  1. sbis

    sbis New Member


    Appreciate without sight of the system, it's hard to comment and there LOADS of variable, but I'm after a ballpark figure for replacement of a functioning but tired floor standing Potterton Kingfisher II with a suitable combi. Simplistic system, gravity fed 6 radiators, hot and cold water tanks in same cupboard that backs onto boiler.

    Boiler to be moved into airing cupboard (literally other side of wall it's on) with horizontal flue length of 3 metres to existing airbrick and there's a suitable overflow to the drain for the condensate pipe. Powerflush as necessary/stipulated, and some TRV's. Apparently gas supply pipe does not require upgrade.

    Issue is quotes so far have varied from £1445 to an eye watering £6000, and excluding the boiler and replacement rad costs I just can't reconcile them. Bexley based, 2 bed purpose built flat if that makes any odds?

    Cheers in advance, hugely appreciated.
  2. Teuchter

    Teuchter New Member

    Let me guess, now - was the £6k quote from BG?

    Including the power-flush, £1.5k upwards to, ooh, £2k - perhaps a little more - would be about right. Yours sounds like one of the simpler conversions, with no need to crawl around in lofts to remove the old tanks.

    Choose a good boiler, although that will make the main difference in your quotes.
  3. sbis

    sbis New Member

    Terrific, that's really helpful - £6k was from a national, not BG but don't know what the score is on naming (and quite frankly shaming!) on here. Consensus amongst all that have been to look is it's 'dead simple', so why the big quote differential. Am I getting materially better solution by forking out more cash, I'm not flush but don't want to skimp and regret.

    Anyone any thoughts on Vokera combi boilers?

    Thanks again.
  4. Teuchter

    Teuchter New Member

    Absolutely no reason not to name the 'national' company involved with that quote. It's not slanderous - you are simply stating how much it was.

    As for Vokera - I just dunno about them. Others on here will hopefully advise.

    What you will likely find is that many plumbers will have their particular 'favourites' and will recommend that make. Nothing wrong with that; there are plenty good makes to choose from, and the plumber will have lots of experience fitting that particular make and will likely also have good relations with the supplier should any problems arise. But, don't allow them to 'push' a boiler you are not happy with...!

    If in doubt, list the makes and models of the boilers suggested by the various plumbers on here, and any 'no-nos' will soon be picked up on.

    Did the plumbers do a test of your mains water pressure and flow rate? I hope so. Treat with more caution any that didn't.

    Also, choose the largest (within reason!) boiler you can get away with cost-wise - that'll give you a better flow rate. I know you only have 6 rads - which would normally suggest a 'smaller' boiler - but even powerful modern condensing boilers will 'modulate down' the power to the Central Heating side to cope with only a few rads, but will then have power in reserve when heating your DHW to give you a good flow. Provided your cold mains can delivery it, of course...

    I'd suggest you ideally want 12 litres per minute upwards.

    So, worth posting the makes AND models of the boilers you are considering on here.
  5. tomplum

    tomplum Active Member

    i am known to recommend baxi's, many disaree, which magazine agrees with me so they can't be too far wrong, they're moderate price, good water delivery, dependable as any other,and when they do go wrong ( and they all do) they have a great back up team, heateam, who have an army of engineers carrying spareparts ,
    an easy installation in my area would be upwards of £1400.
  6. sbis

    sbis New Member

    Cheers, this is really very hepful - slightly concerned that nobody has tested the mains pressure yet as I've watched as they've walked around!

    Npower (with 5yr warranty) are dearest, then Northern Gas, then a free-ads local company and finally cheapeast is on a recommendation from friends. Cheapest install is a Vizo 24 boiler, 2nd cheapest is 'Vokeira Jr' (can't read handwriting) and the other two just quote SEDBUK A rated condensing boiler.

    Preferrsed quote is £2650

    £1100 Vokeira Jr boiler including flue
    £400 powerflush
    £180 TRV
    £150 2x new radiators
    £390 consummables (I'd like a bit more detail what this is)

    remainder is labour, and no mention of VAT but told it's included. 2yr manufacturer warranty on install. £82/anunum thereafter.

    tomplum - Baxi was my preference, purely based on the fact old house with Baxi boiler only ever needed servicing in 12ish years.

    Time and input appreciated.
  7. fitero

    fitero New Member

    We have had a Vokera 35E condenser/combi for two years.Serviced by Vokera [1st year for two year warranty conditions]and 2nd year service today by mate[Gas safe]He says its running perfectly,no soot and still set up spot on manufacurers spec,£50 thank you.
  8. Teuchter

    Teuchter New Member

    Sbis, where are you located?

    Bottom line - you decide which boiler they fit. Can't comment on the Vok as I'm not a plumber

    A bit concerned about the 'jr' bit - do you know what its spec is?

    Oh, and they'll all need to be Sedbuk A rated - so that's no help! Surprised they haven't mentioned makes/models.

    I'm astonished that they haven't talked the whole thing through with you in more detail. Perhaps the water flow issue is a given, if the supply in your locality is known to be good, for example. But still...

    'Consumables' are pipes, fittings, flushing liquids, inhibitor, sandwiches, etc. Can't comment on price, but is probably in the right ballpark.

    Overall, tho', £2.65k is on the 'highish' side, imo, so if you aren't in London or similar, then make sure you get the best bludy boiler there is for that money...

    Decent makes include Vaillant, Bosch, Baxi; I have a GlowWorm (same co as Vaillant) and I'm pleased with it.

    (PS. don't bother about extending the warranty - chances are it'll go on for at least 5 years without any hiccups at all, and even then whatever goes wrong will be a cheap repair. Major problems are rare these days.)

    Personally, recommendation by friends - as long as you trust their judgement - is usually the best way to go. This was the cheapest - so ask him to quote for a better boiler.

    Don't forget: flow rate, flow rate, flow rate...
  9. sbis

    sbis New Member

    Hi Teuchter - great stuff, getting a bit more confidence here, thanks!! I had someone else out last night that tested mains water pressure at 26litres per minute, advised based on area that the flat requires 33,000btu's to heat and recommended a 24kw Potterton Economy Perfoma Eco HE (others have recommended higher than this). Replacing no rads, one room switch and 5 TRV's. Quoted £3500 including warranty but not making good/getting rid of old stuff afterwards and chemical flush only (reckoned powerflush more harm than good).

    I'm in Bexley, so a London Borough, but hardly central London - does it make that much of a difference to the price?

    Recommendation can't do the job until after Christmas and if I'm being picky, I'm sure the installation is perfectly safe, but cosmetically it's pretty untidy. They have no paperwork either, which is possibly a concern for us as we're planning to sell and assume would have to show some paperwork to authenticate the install as legit?

    Really didn't think it would be this much hassle!
  10. tomplum

    tomplum Active Member

    you're darn tootin (plumbrs jargon means absolutly right )about the paperwork sbis, he needs to be gassafe reg, so that he can notify the job when complete and you will be issued with a certificate thatis needed when selling the house,
  11. Teuchter

    Teuchter New Member

    Sbis, yes, it can be absolutely astonishing how what should be a simple task turns out to be a paininthearse before it even starts. I had a similar situation about 5 years ago - called 5 plumbers in total for quotes - some because the first ones never appeared; only 3 came finally came out to quote for a similar job to yours (vented to combi system). Of these, I wouldn't have given 2 of them the job had they paid me.

    Typical attitude was lack of communication/discussion of my requirements, a presumption that I was an idiot who knew nothing about plumbing when I did try and diuscuss the job (typical example was when they recommend their own particular fav boiler, and I asked about an alternative which I preferred; one simply tried to dismiss my choice by saying "it wasn't Sebuk A rated", so I had the embarrassing task of telling him that "yes it was", and further it had a SS exchanger (which 'his' didn't), a central burner (ditto) and a better reputation, etc). Then there's the kicking of pipes (I didn't think even 2nd-hand car salesmen did that these days), the "Oh you don't want your boiler moved there..." Er, yes I do, etc etc.

    Phew, got that out of my system - I hadn't realised it had left scars...

    Anyways, 26 lpm?!!! Jeepers, your garden hose must be like a power washer? That's a fab pressure - and will be completely WASTED by a crappy 24kw boiler that can only deliver less than 10 lpm. ***, what are these plumbers on? (And that Potterton is just a sub-£600 box - you can do better...)

    The main 'problem' with combi boilers - apart from that they are more complicated and therefore more likely to go wrong - is the poor hot water flow rate compared to that from stored, vented, systems. However, that shouldn't be too much of a problem if you go for a decent boiler size. I have a 30kw machine which delivers powerful showers, a nice splashy hot flow at the kitchen sink, and fills a bath in 5-10 minutes (It's around 14 lpm). Ok, it won't cope with having 2 hot taps on at the same time - the flow drops off a huge amount. However, this is hardly ever a problem. (I wish a little I'd gone for the 38CXi - wooooooo - but I'm still happy with my little GlowWorm 30CXi...)

    Ok, this is my personal opinion, of course, but it's based on my experience, my research and also following many threads on here: You'd be simply NUTS to go for a boiler of less than 30kw output.

    This size of boiler will NOT be 'too powerful' for your heating system as they 'modulate' to adapt to the demand (the boiler burner will turn down - just like the burner on your hob - to give just the right amount of heat to the rads). Mine, I believe, will modulate right down to 5kw - just enough for a couple of rads...

    Something else I'd suggest you think about is the new rads you are planning to fit. Why are you changing them and WHERE are they going? If they are going to be located in the main living area, then I would personally fit either slightly larger ones, or ones the same size but with more output - ie: go to 'double panel' instead of single, etc. The reason for this is that you should be able to run your boiler with a cooler flow temp to the rads and still get the same heat out of the rads as before (since they're bigger). This will mean that the return temp to the boiler will also be less which means it will 'condense' the flue gas more = more efficiency.

    Ok, it won't be the biggest change in the world - and your new boiler will already be oodles better than your old one - but, if you are replacing the rads anyway, that wouldn't be a bad move ('every little helps...')

    So, you SHOULD be able to get a good quality, more powerful boiler fitted for around the, say £2.5k mark. No question. Treat with caution any quotes significantly above this.

    Also, when you talk to plumbers and try and discuss matters such as my points above, see how they respond.

    If I were a plumber, I know that I'd be happy - nay, I'd insist - they talk about the 'detail'.

    Suggestion: make up a guest room, and invite Mr Tomplum down for a few days to do the job.

    (Plumbing in t'day, singsong in t'evenings...)
  12. Teuchter

    Teuchter New Member

    Oh, and "powerflush more harm than good..."!

    That's rubbish.

    To be honest, it depends on the condition of your existing system - if it's always had inhibitor in it and the system water is very clean, then quite possible you won't need a power flush.

    However, £3.5k for that tiny boiler, no rads, no powerflush...?! Jeepers.

    Absolutely ridiculous.

    The reason why your system needs to be really clean before fitting a new condensing boiler is that the heater matrix - where the water passes through to be heated by the burner - is much, much finer than in traditional boilers. Any sediment present in your pipes and rads - which will be shaken up by the new install - is more likely to bloke these tiny bores.

    A through clean can be essential. I understand that some manufacturers insist on it for warranty reasons.

    Make up that spare room...
  13. sbis

    sbis New Member

    Teuchter I'm glad my heating predicament has encouraged the vent - heading for a similar experience I think! Also funny you should mention the guest room as it has already been offered to a family friend who installs in Sheffield, I've even offered to put him up in a hotel/cover his travel but he's simply too busy.

    Pressure is terrific (even at the first floor), and I asked the plumber last night whether the boiler would somehow reduce this and he answered no - assume this aint correct?

    I'm happy to do the boiler research on the basis of your recommendations, all sensible stuff – I’ll supply it or pay someone else's markup, but I'm still stumped without a fitter - shame there isn't a recommended trades section on this site!?

    No real reason to change the rads as they’re working without cold spots and there’s no corrosion, but I was advised it would be sensible to upgrade the 2 in the living room as there is a large double glazed picture window in there. Only issue is all radiator pipes exit up form a concrete floor so assuming the new rads would need to be a similar size, as Mrs will spew if there is a total redec involved on top – I don’t want to change the location of anything, save for the boiler which is moving a brick’s width away!

    Liking the idea of the improved efficiency, and if the two of us become three as anticipated it would be great to be able to regulate the temperatures in the bedrooms.

    Will try get some more informed quotes – having similar issues with people seemingly interested, then just not turning up! Credit crunch? Not round my way!

  14. sbis

    sbis New Member

    Changed bathroom rad to a heated towel jobby recently, and the water isn't sludgy - it's a browny colour but certainly not clear. System is late 70's so imagine it's not super healthy, but touch wood no issues to date.

    I'll see what the next chap has to say tonight, just wish I could do some of this myself then get someone in to do the bits I can't!

  15. Teuchter

    Teuchter New Member

    Hmmm, you ain't going to get 26 lpm out of your hot tap! And I doubt you'd want to... Even if you did, it would be pretty luke-warm.

    With that kind of flow rate, a restrictor will likely be fitted in the boiler inlet; if the actual water pressure is also high - which it's likely to be - then a PRV should really be fitted in the cold mains feed and tweaked down to 3-ish bar.

    Your cold taps - currently fed by from a stored tank - will come to life! They'll all be like your kitchen cold tap.

    Hard to tell what you system water is like - the colour is only half a clue - there could be sediment sitting at the bottoms of the rads just waiting to shift... Hence a power-flush is best.

    What size and TYPE of rads are currently in the living room? Could they be 'upgraded' without actually changing their physical size?

    Wigan ain't far away - time to ask Mr Tomplum...
  16. tomplum

    tomplum Active Member

    thank you mr teuchter for your continued 'advocate'ing ;) i am honoured and flattered by your confidence in me, however there is little or nothing i can add to your comprensive advise on boiler choice and dealing with other plumbers wanting to do it their way, i would love the chance to emigrate south for a few days and soak in the smells and tastes of life in the richer half, but like the op's shefield plumber, i have plenty to do up here,
    but once again i thank you your advertizement and promise to send you a free drink in the form of a perferated pyramid shaped bag that needs only a small amount of boiling water and milk and sugar to make a refreshing and welcoming drink should you furnish me with your postal address,
  17. Teuchter

    Teuchter New Member

    Why, certainly.


    Mr Teuchter
    c/o His High Horse
    The Moon.

    My throat is croaking in anticipation...
  18. Captain Leaky

    Captain Leaky New Member


    They only drink cider in Devon. ;)
  19. Teuchter

    Teuchter New Member

    You anywhere near Bexley, Cap'n, perchance...?
  20. Captain Leaky

    Captain Leaky New Member


    Poole , Dorset - where all the millionaires ( and me ) live. ;)

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