Oil Combi Boilers

Alfster Posts: 60
First Anniversary Name Dropper First Post

We currently have a Grant condensing oil boiler. There are a few inconveniences about the boiler. Firstly, it is in the cellar and would prefer it outside. Secondly, we have large cold water storage tanks and a hot water cylinder in a cupboard in the main bathroom taking up a lot of space.

I was wondering about (probably long term) whether it would be a good idea to switch to an oil combi. If this could then go outside it would free up so much space in the main bathroom (and cellar). What are people’s thoughts on combi oil boilers vs standard condensing ones? Would this be a wise long term change when current boiler has seen better days? 



  • Apodemus
    Apodemus Posts: 3,384
    First Anniversary Name Dropper First Post Combo Breaker
    I would give this a "Yes...and no" answer.

    The combi probably wouldn't be much more efficient than the existing condensing boiler, so the cost of replacement would need to be valued in terms of the space saved (and reduction of leak risk), with no prospect of actual payback.

    The longer term scenario needs to factor in the likely prohibition on new fossil-fuel boilers (except for particular exceptions) and if the house subsequently needed to be converted to a heat pump or an electric hot-water system, you would need to be able to reinstate your hot-water tank, with the loss of the space saved by the combi.
  • Reed_Richards
    Reed_Richards Posts: 3,978
    First Post Name Dropper First Anniversary Combo Breaker
    edited 5 March 2023 at 5:31PM
    You are comparing a vented hot water system (I think from your description) with a combi that would supply mains pressure hot water but you could consider an unvented hot water cylinder and therefore no cold water storage tanks.

    As @Apodemus says, the days of combi boilers may be numbered.

    I used to have a combi oil boiler that was outside.  But it was plumbed to carry the hot water to the middle of the house where the cylinder had been previously and then from there to the hot taps.  This made for hugely long pipe runs and so a really unpleasantly long wait to get any hot water out of a hot tap.  
Meet your Ambassadors


  • All Categories
  • 341.6K Banking & Borrowing
  • 249.7K Reduce Debt & Boost Income
  • 449K Spending & Discounts
  • 233.8K Work, Benefits & Business
  • 605.9K Mortgages, Homes & Bills
  • 172.3K Life & Family
  • 246.5K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 15.8K Discuss & Feedback
  • 15.1K Coronavirus Support Boards