Combi boiler thoughts?

poledancer49

Hello all,

Sold our house and have bought a Victorian property. It has a combi boiler...never had one of those...are they any good to run central heating, hot water and one shower? Just curious really

benjus

I'm sure there are better options available out there, but I certainly prefer a combi boiler to the traditional setup with a cold water tank, hot water tank and water heated on a timer. They are certainly capable of providing a decent shower.

slopemaster

My 20+ year old one works fine and is even quite economical.

poledancer49

I like the economical bit....bills sooo high at the mo.

ChumpusRex

Combi boilers are generally OK.

If you are used to a traditional "stored hot water" system, there are a few minor differences with combis.

1. A combi will never "run out" of hot water, as the water is heated on demand.

2. There will be a delay of a few seconds when you turn on a hot-water tap, before the boiler fires up, and then about 30-60 seconds before the boiler has warmed up enough to heat the water to a good temperature. This is usually noticeably longer than it takes for hot water to start flowing in a stored system. If the combi is small, you may find you need to turn the tap on full, to get the boiler to fire, then turn it down to a trickle to allow the boiler to warm up, before opening the tap fully again. A decent house sized combi shouldn't have this problem - but a very small combi unit, e.g. for a flat, may have this problem.

3. Combis are severely affected by changes in hot water demand. If you are showering, and someone else turns on the kitchen hot water tap, the flow of hot water will slow to a trickle, giving an ice cold shower.

4. A combi can't heat the radiators and water at the same time. If you like long showers, then the radiators will go cold while the shower is running. (the radiators will, of course, only cool gradually while the shower is running, and when the shower is turned off, they will immediately start re-heating, so by the time you've finished drying yourself, the radiators should be warm again - in reality, this is a very minor point).

5. Not all combis can regulate the temperature of the hot water. The ability to regulate water temperature is a feature called "full-modulation". Some combis are "step modulating" or "partial modulating". Step-modulating combis work by allowing the temperature of the hot water to vary between scaliding hot and ice cold. This works fine for filling a bath or a sink. However, step-modulating combis cannot be used for showers (for obvious reasons). If you have a combi boiler but shower temperature fluctuates like mad, you may have a step modulating combi - if you do, you can't fix the shower. The only options are to replace the boiler for a fully modulating combi or replace the shower for an electric shower.

6. The hot water is at high pressure (at least if all you are doing is using 1 shower). This allows a vigorous shower. The flow rate for combi heated showers is generally better than the old-fashioned gravity-powered stored hot water systems. However, the performance of a combi powered shower is nowhere near as good as a pumped stored hot water system or a pressurised stored hot water system.

7. There are some energy savings with a combi. A hot water tank "leaks" about 10 p worth of heat per day. With a combi, there is no stored water, so you save this money. [Note that this is only a minor energy saving. By far the biggest energy savings for a boiler come from switching from a boiler with a pilot light, to one with electronic ignition - a pilot light costs 50p - £1 per day, just to have the boiler on standby]

8. No backup hot water supply in case of boiler breakdown. If a stored-water heating system packs-up. There will be an electric immersion heater which can be used for emergency hot water. With a combi, there is no backup option, other than heating water in a pot on the hob.

benjus

ChumpusRex wrote: »

6. The hot water is at high pressure (at least if all you are doing is using 1 shower). This allows a vigorous shower. The flow rate for combi heated showers is generally better than the old-fashioned gravity-powered stored hot water systems. However, the performance of a combi powered shower is nowhere near as good as a pumped stored hot water system

I disagree. I've had experience with several different pumped stored hot water systems and combi-based systems, and my experience is that the showers in the combi-based systems are just as good.

poledancer49

Wow.....thanks ChampusRex...thanks for the time spent in providing me with this information....will read and absorb.

ValHaller

ChumpusRex wrote: »

Combi boilers are generally OK.

If you are used to a traditional "stored hot water" system, there are a few minor differences with combis.

9. Their performance in delivering hot water can be quite poor if the water pressure or flow rate is not good.