St Margarets plumber

Combi boilers work for many people, but they have so many drawbacks that it's hard to remember them all at once, but people keep asking me what the problems are so here's a quickly compiled list for starters...

1) They are obviously more complex than system boiler, so when stuff goes wrong, they are more difficult to diagnose and repair.  

2) Water scale. They scale up just like an electric shower does. Then you have to buy a new heat exchanger or pay for a descale every year or three. Several hundred quid either way. (But note! The Worcester CD range of boilers have a 'plate to plate' heat exchanger designed to overcome this problem. Worcester guarantees the plate heat exchanger for 10 years 

The difference is, Worcester seems happy to send us a free new one every 18 months under guarantee, so if you MUST buy a combi, buy a Worcester)

3) Latency. When you turn on the kitchen tap, it takes about 30 seconds for the hot water to arrive. Only after you turn on the tap does the boiler fire and start to warm up. It warms very quickly but it's still much slower than having a tank of hot water connected to your hot tap.

5) Water pressure. They are great when your water pressure is high but come the summer evenings when everybody puts their hose pipes on to water the gardens, pressure drops. 

6) Showers again. Performance of showers connected to combis is pretty average. Not bad, and not brilliant. Problem is, if you want a better shower, you are stuck. 

You have to fit a bigger combi, and then the performance won't be that much better. Adding a pump just doesn't work. The boiler itself is limiting water flow so it can deliver the temperature your shower needs.

7) Combi boilers have pressurised sealed system central heating circuits. This means that a very slow water leak from your heating system (and these are VERY common) will cause your system pressure to degrade to zero over weeks or months, and these leaks can be fiendishly difficult to identify and fix. The old way of having a header tank in the loft gets around this problem, but combis are not designed for use with them.

8) Redundancy. You need some! With a conventional boiler/hot water cylinder system if the boiler breaks down you can still have hot water by turning on the immersion heater in the hot water cylinder. 

When a combi breaks down, heating AND hot water are usually both out of action until it is repaired.

If you understand these potential issues and are happy, they don't apply to you, or you are happy to take the risk to obtain the benefits of having no bulky water storage tanks in your home then there is no reason not to buy a combi!