When my husband was a gas engineer, he used to do what were known as foreigners. This didn't mean he beat up immigrants, it meant taking on jobs outside of normal work. I think other expressions for it is are on the side (but I don't like that one!), or thumbers. Him and a chum would fit central heating for people. They only had one hard and fast rule - the only make of boiler they would fit was Vaillant. (Everyone pronounces this VALIANT, but it is pronounced VAY-LANT - sorry, that's just me being pedantic). The reason for this? Vaillant were the only boilers that they could rely on not to break down. They didn’t want to have to go back repairing the thing, so they only fitted Vaillant boilers, which came with a good guarantee and a lifetime of excellent boiling (or whatever boilers actually do). If it was an elderly person who really couldn’t afford a Vaillant, they would consider fitting a Worcester, which are nearly as good (see my separate review on Worcesters).
Vaillant boilers are not cheap. They are one of the most expensive in the boiler market, but are a classic example of getting what you pay for. In price, they range from around £650 to £900 - at trade prices. Then you have fitting to pay for on top of that -around £1400-£1900 for a boiler swap on an existing system. You could possibly get one fitted cheaper but for a decent job, you are looking at those prices.
Vaillant are a German make, excellent quality and workmanship. They are substantial, not the prettiest boiler in the world and a little bit larger than most combination boilers, but second-to-none for reliability.
Combination boilers heat water so rapidly that the hot water calorifier scales up with limescale quickly. But Vaillant guarantee that theirs won’t for at least 5 years. My husband has replaced them on other good-quality boilers in semi hard water areas after just 2 years. You don’t really want to be replacing a part that costs over £100 (plus fitting) every couple of years. This is even more of a problem on cheaper boilers. Water softeners, such as lime fighters, do help, but they are only of any use at all if they are fitted within 3 feet of the boiler. This is important. It doesn’t cure the problem but it really helps.
When we moved into our present house, there was quite a good-looking boiler in the kitchen. It was an Ocean. My husband says Ocean boilers should be described as sprinkler systems rather than boilers. Ocean have now changed their name to Alpha in an attempt to improve their reputation. It might have been better if they had just improved their boilers. It is things like those that get combination boilers a bad reputation. Our little Ocean was ripped out after a couple of weeks and replaced with a huge Vaillant. The new one has been in for 3 years now without a hiccup and we had one in our last house for 8 years without any problems. I think it is big and ugly, but my husband looks at it with the sort of admiration he normally reserves for Saabs, Ferraris and Californian women.
People will often refer to British Gas to see what boilers they supply, as an indication of quality. They don’t supply Vaillants normally but will fit one if you absolutely insist. The reason for this is Vaillant refuse to sell their boilers much cheaper to British Gas because they don’t have to - their boilers sell on their reputation anyway. British Gas like to make a good profit, so won’t bother with Vaillant as they don’t make enough.