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Old boiler advice - replace or not

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  • Also there's the chance that fuel prices might go up in coming years as the squeeze is put on fossil fuels. 
    Then perhaps its' worth leaving it alone until the point where ASHP and especially GSHP become more cost effective and swap over then.
  • grumbler said:

    My understanding is that mains water goes through the 'secondary' heat exchanger where it's heated by both the circulating hot water (going through the 'main' heat exchanger) and flue gases.

    Condensing Boiler Condensing Boiler Piping Schematic


    That pic isn't a condensing boiler 
    I'm only here while I wait for Corrie to start.

    You get no BS from me & if I think you are wrong I WILL tell you.
  • grumbler
    grumbler Posts: 58,629 Forumite
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    edited 16 January 2021 at 11:23PM
    Later I tried to find a decent scheme of a condensing boiler with a HW circuit, but failed.
  • :-)

    I'm pretty certain my condensing combi does not have the mains cold taking energy directly from the combustion process, only via the circulating system water as normal. However, it does still condense to some degree as the plume indicates.

    Anyhoo, it's Chaser's call, and I don't think there's a clear answer; pros and cons on either side. Consequences' point above is a good one, as the green revolution will almost certainly pick up a pace, with some significant changes bound to happen over the next 10 years. But I certainly wouldn't blame him if he simply wanted to go new and more efficient sooner.
  • ratechaser
    ratechaser Posts: 1,674 Forumite
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    I think I may be heading towards information overload now  :)

    Anyway, I'm going to leave alone for the time being - the boiler gets serviced annually and despite its age has never give us any problems. I will ask the question about the overheat stat when BG come round, although if it is a legal requirement for a Megaflo system, I'd hope that it was done as part of the installation.

    Thanks everyone for your advice - and it's reassuring to know that despite being old, it's a very reliable model. Not unlike me...
  • fred246
    fred246 Posts: 3,620 Forumite
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    edited 17 January 2021 at 3:03PM
    Do you have the Megaflo serviced? There is a video here showing the strainer and pressure reducing valve. If the strainer is blocked or the pressure is reduced below 3 bar by a damaged valve you will have low pressure issues.
    https://www.youtube.com/watch?v=n6sK1_diwBw
  • There's every chance that the reason the top floor (3rd...) shower loses a noticeable amount of flow when a shower on a lower flow is also used is just down to physics. Think of it as a vertical pipe fed from the bottom by the mains - a nice healthy spout comes out t'top. Now drill a similar-sized hole in the side half-way down - which one will have the greater flow? What'll happen to the top 'spout'? 

    It basically comes down to (a) just how good - Pressure & Flow - the cold water supply is, and (b) just how much one is drawing from each shower.  I mean, you can't just expect to add additional showers and not see a flow drop in them all.

    Of course there's a chance it's also down to filters and stuff - that should be checked at the next service.

    Assuming, tho', that it's perfectly 'normal' - ie the limitations of this system - what can be done to improve matters? If the incoming mains flow cannot be upgraded, and if there's nothing amiss in the supply pipes, then it's either a case of (a) boosting the cold supply using an accumulator, or (b) balancing what you already have to share it out more evenly.

    For the latter, if the 'below' showers have a stupidly healthy flow, then the H&C isolating valves to them could be tweaked down to 'just' make them 'good' instead. This would mean that the 'top' shower would be less affected when the other ones are also being used.

    (It would have the very appealing additional benefit to Chaser in cutting down the overall hot water use by his kids...). 




  • fred246
    fred246 Posts: 3,620 Forumite
    Sixth Anniversary 1,000 Posts Name Dropper
    The word Megaflo gives it away. Google says that Megaflo can supply 176 litres per minute. A good shower is 20 litres per minute so it should supply 8 showers. If the hot water pressure is at 3 bar it would still be above 2 bar unless the house was taller than 10m which it won't be. All the water goes through the strainer and pressure reducing valve. Clogged up strainer or failed valve likely problem unless inlet pipe is too small or cold water pressure too low.
  • ratechaser
    ratechaser Posts: 1,674 Forumite
    Seventh Anniversary 1,000 Posts Name Dropper
    There's every chance that the reason the top floor (3rd...) shower loses a noticeable amount of flow when a shower on a lower flow is also used is just down to physics. Think of it as a vertical pipe fed from the bottom by the mains - a nice healthy spout comes out t'top. Now drill a similar-sized hole in the side half-way down - which one will have the greater flow? What'll happen to the top 'spout'? 

    It basically comes down to (a) just how good - Pressure & Flow - the cold water supply is, and (b) just how much one is drawing from each shower.  I mean, you can't just expect to add additional showers and not see a flow drop in them all.

    Of course there's a chance it's also down to filters and stuff - that should be checked at the next service.

    Assuming, tho', that it's perfectly 'normal' - ie the limitations of this system - what can be done to improve matters? If the incoming mains flow cannot be upgraded, and if there's nothing amiss in the supply pipes, then it's either a case of (a) boosting the cold supply using an accumulator, or (b) balancing what you already have to share it out more evenly.

    For the latter, if the 'below' showers have a stupidly healthy flow, then the H&C isolating valves to them could be tweaked down to 'just' make them 'good' instead. This would mean that the 'top' shower would be less affected when the other ones are also being used.

    (It would have the very appealing additional benefit to Chaser in cutting down the overall hot water use by his kids...). 




    2 teenage girls. I'd have more luck nailing a jelly to the ceiling.
  • ratechaser
    ratechaser Posts: 1,674 Forumite
    Seventh Anniversary 1,000 Posts Name Dropper
    fred246 said:
    Do you have the Megaflo serviced? There is a video here showing the strainer and pressure reducing valve. If the strainer is blocked or the pressure is reduced below 3 bar by a damaged valve you will have low pressure issues.
    https://www.youtube.com/watch?v=n6sK1_diwBw
    Hmm, I recall that valve being replaced after a year - unnecessarily as it turned out - because we were having leaks and pressure issues. Which in the end turned out to be the 'balloon' in the little pressure vessel (if that's the right terms for it) sitting above the cylinder having burst. 

    The Megaflo itself doesn't get serviced regularly, so something I need to to look into. Honestly, if the shower that is in the room next to the cylinder is use, the top floor shower barely manages a trickle...
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