Can I permanently and safely disable the hot water function of a combi boiler?

Discussion in 'Plumbers' Talk' started by Rocky999, Jan 13, 2020.

  1. Rocky999

    Rocky999 New Member

    I have an Ecotec Pro 28 combi with no storage tank. I would like to have a storage tank and immersion heater installed so I can make better use of my solar PV. I am happy to have electric-only water heating so the hot water function of the boiler is no longer needed (although it might be good to keep it available for emergencies). Would it be enough to fit an isolator in the cold water inlet between the fill loop and the boiler? The system needs to be fully regs compliant.
  2. andy48

    andy48 Active Member

    1. If no one ever used hot water, then the boiler would still run for heating, so the answer to your main question is yes.
    2. If you don't want to use the hot water from the combi, why not fit a decent quality lever valve in the domestic hot water outlet pipe from the boiler?
    3. As gas is about 1/3rd the price of electricity (normal rate), why not fit 2 x two port valves (S plan) and use the central heating output of the boiler to run the central heating (via one valve) and heat the coil in the cylinder (via the other valve) to cut your ongoing costs. You could use a three port valve (Y plan) but I personally prefer the 2 x two port approach.
  3. Rocky999

    Rocky999 New Member

    Thanks for this. Under (1) and possibly (2) I was worried that creating a dead leg of warmish water from the boiler to the hot water taps was a health concern (legionella). Also, if the valve was accidentally opened while the unvented tank was connected, mains pressure hot water would be applied to the output of the boiler; would I need approval from the boiler manufacturer for this configuration in order for this to pass a gas inspection?
    I will look at (3) more closely, as my plumber also suggested it. However my hope is that the over-sized PV system should give me 100% of the hot water for most of the year, so the electricity savings (£30 each January?) have to be set against the cost of the extra plumbing, controllers and motorized valves (£500?).
  4. Jimbo

    Jimbo Screwfix Select

    The solar system could be used to heat a dual-circuit thermal store (i.e. cylinder) near the boiler and put one of the circuits on the cold water line in to the boiler, hence pre-heating the fresh water on the way through, and the other on the return to the boiler, doing the same for the heating. This way everything stays as it is (minimum effort and minimum plumbing) and the EcoTech will modulate down or up depending on the availability of the hot water in the store.

    Maybe looking at battery storage might be a better option.
    Last edited: Jan 14, 2020
  5. Rocky999

    Rocky999 New Member

    Jimbo- Nice idea but unfortunately Vaillant say that the Ecotec must not be used with pre-heated water so it is not an option. I wish I had thought about the future when I chose the boiler! You could be right about the battery.
  6. Jimbo

    Jimbo Screwfix Select

    ...yet they sell a flu gass heat recovery preheater for it...
  7. The Teach

    The Teach Screwfix Select

    Just have 1 hot water tap running from the gas combination boiler,many reasons why including 'appliance intended use'

    Others will offer answers but its down to the person doing the alteration to ensure the boiler and its system is fitted/altered or commissioned to the boiler manufactures instructions.

    What does your heating technician recommend ?
  8. Rocky999

    Rocky999 New Member

    • "One Gledhill 300 litre StainlessLite indirect unvented cylinder with 2 x immersions

    • One Cal mag 22mm inline magnetic scale reducer

    • One Drayton Lifestyle single channel programmer

    • Two Drayton zone valves for heating & hot water

    • Alter boiler pipework and run new flow & return pipework to indirect cylinder

    • Alter system wiring to an S-Plan

    • Connect on to existing hot & cold pipework

    • Run D2 discharge pipe outside and fit guard

    • Register unvented cylinder with Gas Safe for building regulation"
    Presumably the "hot water zone valve" diverts radiator water to the tank on a timer and the combi hot water is...left?...capped?
  9. The Teach

    The Teach Screwfix Select

    Anymore more bullet points for consideration ?

    if not your installer (who is clued up on this boiler) will need to ensure their alteration is the absolute best practice and be able to leave documentation to back up their actions.

    Why not get a gas boiler that is suitable for your intended use,rather than converting an existing combination gas boiler. you know it makes sense ;)
  10. Rocky999

    Rocky999 New Member

    The bullet points are from the quote. I was about to go with it when I noticed he hadn't said what he would do with the hot water, hence the research. Also didn't mention that the tank PRV might cock up my shower unless I replumb it from the balanced output. He also pointed out that the cold fill should have come off before the water softener, which is funny since he installed the boiler 4 years ago.

    Why not replace boiler: Cost really. New boiler+tank+plumbing=4K? 5K? New tank+a few valves=1.5K. Plus it is a bit galling to replace a 4 year old perfectly working boiler.
  11. The Teach

    The Teach Screwfix Select

    Yes i agree :)

    But what is the intended use of your combination gas boiler ? Other boilers are available for your new intended use. Maybe your heating technician will adapt the combination boiler without telling you how-trade secrets :cool:

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