Overview and History of Combination Boilers

Advantages and Disadvantages - Where and where not to fit a Combination Boiler

In the early days of the combination boiler, many thought it would be a passing phase, which would be here today and gone tomorrow. How wrong they were!

Originally the ‘combination boiler’ was an import from Europe where it had been used widely before it caught on in Britain, although as we will see some would argue it’s basic origin was indeed British.

The central heating market in Britain was one where an open vented system, with a capacity to store an amount of domestic hot water was the norm and so when a system which stored no domestic hot water and had a sealed central heating system came along it was seen as a totally ‘Foreign’ concept.

So who had the first combination boiler ?

There are a few contenders for this title one of, which was Junkers whose British arm of the company was Ascot, (The British Link) who around the time of World War 2 turned out its first multipoint gas wall heater. The story then goes that the Germans used the idea of the multipoint water heater and added to it the central heating boiler to produce a combined water heater and central heating boiler all in one unit.

The German giant Vaillant were certainly one of the first if not the first to produce a combination boiler in the early 1960’s and another firm who were in on the act early was a French firm called Chaffoteaux producing their first real combination boiler around 1963.

Where were the British I hear you cry ?

The plain and simple answer was no where at this stage. The British market was firmly fixed to the open vented central heating system with stored hot water and would remain this way for many years to come.

British manufacturers were aware of what was happening in Europe and in the 1970’s a number of them had a stab at the combination boiler, but it was not until the late 1970’s when the imports started to arrive that the British manufacturers really started to take notice.

Even though the imports had started to arrive, it was only a trickle at this stage and one of the main problems was that a mains water connection to a central heating system was simply not permitted and the use of make up bottles and the like were seen as a poor alternative. A change in water regulations in the 80’s to allow a temporary mains ‘filling loop connection’ to be made to the mains water supply was exactly what the combination boiler market had been waiting for.

The British manufacturers were now in a position of a central heating market ready for take off and little or no British made boilers to fill the gap.

The development to produce a completely new boiler over night was impossible so there were two basic options. Firstly buy in a foreign boiler and stick on your own badges and livery and option two was to take your biggest central heating boiler, buy in some foreign hardware bolt it on and call the result a combination boiler.

Both options were tried with rather predictable results but at least the British manufacturers had at last entered the gas combination boiler market but it was not until around 1984 that some of the major British manufacturers marketed their own combination boilers and even later for others.

There are now countless British manufacturers with their ‘own’ combination boilers as the market has grown and continues to do so.

Not only do the manufacturers have combination boilers to sell in Britain but are nowadays exporting them to Europe!

The Advantages and Disadvantages

There are advantages and disadvantages for both the customer and the heating engineer but the main advantages are for the heating engineer.

Advantages for the Heating Engineer

Advantages for the Customer

The Disadvantages

The main perceived disadvantage of a combination boiler as far as the customer is concerned is lack of hot water flow rate at the tap compared with a conventional gravity fed system.

The fact that cold mains water is being heated from cold on demand means that flow rate has to be restricted to allow enough heat to be transferred into the water to produce the hot water at the correct temperature at the tap.

More recently manufacturers have started to produce combination boilers which store a quantity of preheated hot water within the boiler itself and thereby allowing an increase in flow rates on certain models as well as a more rapid delivery of hot water to the tap.

In order to avoid a customer being disappointed in the delivery of hot from their newly installed combination boilers, the issue of flow rates and length of time for the hot water to reach a particular tap must be covered at the initial design stage. The question of flow rates and length of delivery time is rarely of any concern to a customer who has a multipoint gas water heater as the flow rate of the combination boiler would be very similar to that of the water heater.

A second and less obvious draw back is that if the boiler was to fail to function then there would be no back up hot water supply to draw on (no electric immersion heater back up available).

The major disadvantage as far as the installer is concerned is the preconceived idea that the combination boiler is ‘too complicated to repair’. (In due course it will be seen this is not the case).

Where and where not to fit a Combination Boiler

The correct application of the combination boiler is most important, as an ill-fitted boiler will cause untold problems.

The mere fact that most combination boilers have the same output available to the central heating circuit as the domestic hot water can lead to the installation of the boiler in situations which are totally inappropriate for their use.

In a larger than average property the boiler would be suitable for the heating circuit but where numerous hot water outlets or where more than one outlet at a time is likely to be used it would not be suited. (E.G. If a downstairs tap was in use while the shower was in use upstairs the flow rate at the shower outlet would be little more than a trickle).

Another application problem that can occur is when a combination boiler is used as a replacement boiler on an existing system. The radiator valves, pipework and fittings would be subjected to an increased system pressure of two to three times of that before the system was pressurised and thereby lead to an increased risk of water leaks.

Many combination boilers incorporate a low water pressure switch which cause the boiler not to operate if the system pressure is too low for instance if there were a water leak on the system due to inadequate radiators. This would lead the customer to blame the boiler when the actual cause would be down to poor design.

Generally Accepted Sites for Combination Boilers

Generally Unacceptable Sites for Combination Boilers

The exception to the above locations would be if the combination boiler were linked to a storage facility (cylinder). When this type of system is adopted it can be seen to defeat the object of the exercise.