is a combi bolier the way to go.
Most people seem to think combi's are some sort of panacea, without really looking into it. They do have their place (mainly new builds, or very old installations, say pre 1980's when the entire system is in need of replacing) but they're not always the best solution for everyone. Traditional open vented boilers also condense and are available with the same 'A' efficiency rating as a combi, so that's not an issue. Here are 11 reasons why if you have an existing open vented installation a combi might not be for you.
1. Assuming you have modern controls with motorised valves, room & cylinder thermostats you can keep them. Have a combi and most will have to be removed. De-commissioning wiring safely is not always easy, install an open vented boiler and the existing wiring can remain unchanged.
2. Combi’s are more complicated than standard boilers so they have more components inside thus increasing the possibility of a failure. They are not suitable for DIY work. Repairs should be carried out by suitably qualified people and with parts from the manufacturer. On the other hand, open vented boilers have a lot of components externally mounted. Pump, motorised valve, programmer etc., these can be easily replaced by a competent DIYer or local plumber, and with any manufacturers parts obtainable from local plumbers merchants or DIY stores.
3. Combi’s are slower to get hot water to the taps if the boiler is starting from cold when a tap is turned on. Running cold water whilst you wait for it to get hot also wastes water. You could of course use the preheat setting that fires the boiler every so often to keep it warm just in case you need some hot water (a bit like starting up your car every half hour to keep it warm, should you want to go out)
4. To generate hot water directly from the cold mains supply, Combi boilers have a large gas burner. Because of this, you will most likely have to have a larger diameter gas pipe to the boiler to cope with the higher demand. Often in boiler upgrades, this unsightly pipe is routed around the outside of the house.
5. You won't have to get rid of your existing hot water cylinder and feed tanks, which will speed installation and be less disruptive. (This may be a disadvantage though if you're desperate for the few feet of space the cylinder occupies) and you retain a useful airing cupboard for er..airing clothes, making yoghurt or whatever.
6. Combi boilers cannot provide hot water and heating at the same time. When running hot water the heating will go off.
7. With a standard boiler, you can have an immersion heater to provide hot water when the boiler fails (and they do fail, checkout this forum) with a combi it’s the kettle & saucepans.
8. If you bleed the radiators with a combi you will have to manually re-pressurise the system, non system boilers will be automatically topped up from the header tank.
9. Hot water flow from a combi is reduced when cold water is used at the same time, because both are supplied via the same cold main supply pipe. This doesn't happen with a traditional system as the hot water cylinder is supplied from a storage tank which will contain sufficient water to cope with most periods of increased cold water demand, such as when a WC is flushed.
10. Because the incoming cold mains water temperature can fall by 10 degrees in winter the quantity of hot water produced by a combi also falls, but with a traditional system, hot water temperature is controlled by a thermostat on the cylinder, so temperature and flow will be consistent all year around.
11. Just because everyone else is having a combi doesn't mean you have to or it's the best way for everyone (think endowment mortgages in the 1980's)
