New Heat only boilers?

Discussion in 'Engineers' Talk' started by pooface99, Dec 21, 2022.

  1. pooface99

    pooface99 New Member

    I have an old heat only boiler, D rated. I wanted to replace it with another heat only boiler. I am happy with the rest of the system and wish to keep it all as-is.
    However, most gas fitters don't seem interested and only want to fit a combi.
    My house is a 2up 2down end of terrace.

    Is there any legal restriction on fitting heat only boilers?
     
  2. Mike83

    Mike83 Screwfix Select

    Very common still.
    Plenty get fitted in new builds.
    Find a decent installer.
    Installer works for you and fits what boiler type you prefer.
     
    Kingscurate likes this.
  3. quasar9

    quasar9 Screwfix Select

    Look for system boilers. Plenty about at every price point.
     
  4. pooface99

    pooface99 New Member

    Thanks, what would be the point of the extra work to replace my open vented system with a pressurised system?
     
  5. Kiaora oap

    Kiaora oap Active Member

    Hi
    The glowworm hxi 12 or 18 (if you have a big system)
    Simple to fit, has no pump or expansion vessel,
    Not a lot to go wrong, and the flow return tapping are on the top of the boiler

    good luck
     
  6. quasar9

    quasar9 Screwfix Select

    Not a lot, many system boilers have the EV and pump built in. The only extra work over a combi is either a 3 port valve or 2x 2port valve. As you have a hot water cylinder, these things can fit nicely in the cupboard where the cylinder is.
     
  7. Bob Rathbone

    Bob Rathbone Screwfix Select

    It will show up all of the weeping joints in the current system:(
     
  8. MGW

    MGW Screwfix Select

    Changes old to new is new must be able to gain the latent heat, and to do that they must be able to modulate.

    Closed or open, combi or system, does not matter, but the big change is it monitors return water temperature, so lock shield and TRV and by-pass valves become important.
     
  9. quasar9

    quasar9 Screwfix Select

    I think every boiler on sale in the UK can modulate. At the higher end, the latest models are modulating down to around 15% of their maximum rating, but I suspect this may just lead to lazy installers not sizing the requirement correctly and fitting oversized units.
     
  10. Kiaora oap

    Kiaora oap Active Member

    hi
    Sounds like a dig at installers ?
    It’s not always possible to do things “correctly “

    we just fitted a 18kw heat only boiler to a system that can’t cope with that output,
    But we can go into the board to change it it 12kw
    We couldn’t get a 12kw., so had it improvise

    regards
     
    Kingscurate likes this.
  11. MGW

    MGW Screwfix Select

    I don't think many other than gas powered can modulate, oil don't seem to modulate, and unlikely solid fuel do, as flue temperature is very important to stop particular emissions, I see no reason why a heat pump could not have an inverter drive, so it could modulate, but don't think many do.

    I think modulating boilers is a gas only thing. I think all new gas boilers must modulate, to comply with gaining latent heat from flue gases, but when we moved we expected much higher bills using oil, but in fact they were lower, last top up which will last the year £500.

    The big problem with gas, is your tied to the supplier, the LPG tanks are very expensive, and the suppliers tend to provide them in return to you agreeing to use their supply, second is the danger, I remember the French camp site accident where the road tanker wiped out the site when the tank split. The LPG tank is a bomb in your back garden. It may use less fuel kilojoules wise, but it is more expensive to start with. The same goes for heat pumps, may use less fuel, but fuel more expensive.
    So I assume in this case it is a gas boiler, but so many gas boilers are way over size, this house has a 19 kW oil boiler which is still over sized for my three story house, mothers house only two floors, had a 28 kW gas boiler, why? My old house did not have a DHW store, just two gas boilers, one for central heating, one for domestic hot water, it has since I left been swapped for a combi boiler, but the one for DHW was 18 kW, which was ample, in fact was hard to find shower roses big enough to get the flow required to keep boiler running.

    That old house when built had a single 4.5 kW gas fire to heat whole house, and it did work, even looking at speed to reheat house, you clearly don't use all rooms the minute you arrive home, so in this house want kitchen, dinning room, and living room warm, but the 4 bedrooms upstairs, and the bedroom downstairs, with second living room and kitchen do not need heating at the same time, so the dinning room, living room and kitchen needs to have radiators large enough to sink the 19 kW from the boiler, and they don't, so all the smart programmable TRV heads are wasted. My boiler is always cycling on/off, rarely will it run solid for even an hour, so clearly over sized at 19 kW.
     
  12. quasar9

    quasar9 Screwfix Select

    Obviously I was referring to gas boilers as modulating oil would require a form of fuel injection, for too complex for a domestic boiler. With solid fuel like coal, while technically just possible ( pulverised coal on a fluidised bed boilers) but not in an domestic setting.

    Not having a dig at all installers as there are always cases where theory won’t work and a working solution is required which means making compromises and choices.

    But there is a tendency to overate, some coming from the property owner themselves, as they want to be sure the boiler can cope with worst the weather can throw at us.
     
  13. pooface99

    pooface99 New Member

    Thanks for the info.
    Even my old boiler is modulating, 15kw / 7.5kw but is only D rated because it's not condensing
     
  14. Tilt

    Tilt Screwfix Select

    @pooface99
    No, there are no legal restrictions.
    I had an Ideal H15 heat only fitted about two years ago now.

    Simply replacing a much older non condensing 'heat only' boiler.
    Fitted alongside new timer controls and thermostats and TRV's, including wireless room stat.

    No issues to date. (touch wood).

    The bonus you have with a 'heat only' boiler is that they are more reliable than either 'combi' or 'system boiler' (as less things to go wrong inside) and you can still have hot water (assuming your immersion element works) if your boiler does break down.
     
  15. Jimbo

    Jimbo Screwfix Select

    You might find an air-source heat-pump could be fitted relatively cost effectively in this scenario buy e.g. Octopus.
     
  16. pooface99

    pooface99 New Member

    Not available in my area.
    Unfortunately my old boiler is now broken and still haven't found anyone to fit a new heat only boiler.
    Anyone know someone in Plymouth?
     
  17. Notnowvicar

    Notnowvicar Screwfix Select

    You can use a combi as heat only ...
     
  18. pooface99

    pooface99 New Member

    It's not the boiler that's the problem. It's finding someone to fit it.
     
  19. Tilt

    Tilt Screwfix Select

    If this was in the Outer Hebrides then I could understand struggling to find a gas fitter .......

    Is it really that difficult in Plymouth ???

    There are also Nationwide fitting services I believe ....
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice