Heating System Upgrades

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  • ComicGeek
    ComicGeek Posts: 1,538
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    I have a Vaillant ecofit pure 418 boiler and Gledhill slimline cylinder. I chose not to have a system boiler, personally I prefer to have a separate pump. Mid range units, but easy to get serviced or parts for. 2 years old now.

    Space heating load is only 12 kW for our house (although I have since removed some rads and replaced with air con units, so lower now), so didn't need anything larger.

    If I was designing my system for someone else I would be much more conservative and recommend storage and pump set, but as it was my own I took the risk to save money.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    By 'system' boiler, I just mean one that is sealed, pressurised, unvented. No idea where the pump goes in each!
  • jennifernil
    jennifernil Posts: 5,567
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    edited 7 June 2023 at 9:37PM
    We recently replaced our 34 year old Potterton Neataheat boiler with a Veissmann Vitodens 100W heat only boiler.  We have kept the same vented system as it worked well and gave decent showers, we have 1 bath and 2 showers.   We did fit a new HW cylinder, of the same size, as the back up immersion heater element had failed and could not be removed from the cylinder.

    The system is fully pumped, using 2 pumps rather than a motorised valve, and we have also invested in a tado control system and replaced most of our TRVs with smart TRVs.

    As a result our gas consumption is down by around 35%, and the individual control of each room and the convenience of use is very good.
  • TooCautious
    TooCautious Posts: 21
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    Thanks for all the useful comments from everyone.
  • ComicGeek
    ComicGeek Posts: 1,538
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    By 'system' boiler, I just mean one that is sealed, pressurised, unvented. No idea where the pump goes in each!
    Boiler manufacturers generally group them into:

    1) Regular/open vented (but can still be used in a sealed pressurised system without expansion pipe/tanks) - needs separate circulation pump and expansion vessel.

    2) System boiler with integral circulation pump and expansion vessel. Can sometimes need an additional expansion vessel for larger systems, which largely defeats the whole point of having integral ones IMO.

    3) Combination boiler with integral circulation pump and expansion vessel. 

    When comparing costs between the Vaillant ecofit pure 418 (regular/open vent) and the 618 (system) the system boiler is about £200 more. Personally I prefer having the pump and exp vessel separate for easier maintenance, and being able to pick what products I want.

    I also see a lot of system boilers where the integral expansion vessel isn't large enough and a second expansion vessel is needed anyway.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    Thanks, CC.

    I would personally always go sealed- pressurised for my boiler.
  • BUFF
    BUFF Posts: 2,185
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    fredddddddddddd - I had looked at this Viessmann boiler as a possibility. The downside is that it's a big beast and won't fit in the current location. But worth considering if I can re-site.


    Have you also looked at the Worcester equivalent, the Highflow?
    However, for either the Viessmann or the Worcester you will be limited to the 18lpm incoming even though the boilers are capable of delivering higher flow rates (in the case of a Highflow 550 25lpm @ 40°c ∆T) than 18lpm if the supply can  provide it . 
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    edited 8 June 2023 at 11:22PM
    Have to say, I have done a pretty much 180o U-turn on combi boilers, 'thanks' to this forum. They still have their place, no question, but for anyone future-proofing in terms of wishing to add other forms of energy source, then surely a stored hot water system, possibly even a heat store, is the way to go?
  • BUFF
    BUFF Posts: 2,185
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    edited 9 June 2023 at 9:07AM
    I think that it depends upon what is available to you (i.e. do you have mains gas already/available in street), dhw demand & how long you intend to stay in the building. Not to mention budget. Imo for the next probably 15 years gas condensing  boilers of whatever type are safe, after that we will probably all be on heatpumps which will require dhw storage.

     In those 10-15 years though I think that things are going to change within the heatpump/boiler replacement industry - there is still a lot of learning/product improvement to be done.
  • FreeBear
    FreeBear Posts: 14,217
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    Have to say, I have done a pretty much 180o U-turn on combi boilers, 'thanks' to this forum. They still have their place, no question, but for anyone future-proofing in terms of wishing to add other forms of energy source, then surely a stored hot water system, possibly even a heat store, is the way to go?
    Have a look at the Intergas (combi) boilers - They can be set to either deliver heat only, hot water only, or both. Handy if you need to drain down one circuit and keep the other "live".
    As for future proofing a system, there is a bit more than just contemplating the location/installation of things like heat stores - Larger radiators, bigger pipes, space, and the route of the pipes all come in to play. As part of my CH system upgrade, I've fitted larger radiators, 22mm feed/return pipes (routed to take in to account a possible location of an ASHP). With an eye on fitting a small wood burner with a back boiler, I've also allocated space (and pipework) for a heat exchanger - All this future proofing costs extra on top of the upheaval and work required.

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