Central Heating System Repair – The Result Of A Poor Installation.

08 May. 2019

Written by Neil Marsh MCIPHE RP RHP EngTech

Sixty percent of FORTHRIGHT’s maintenance/repair work would not exist if the work done by others was installed correctly in the first place! If you do not use the right people the first time, it is likely to lead to problems down the line and more than likely will cost you a lot more money…

Sadly, the customers who own the boiler in the photograph above inherited problems with their central heating system after buying their house. The company contracted to replace the boiler was done so by the previous owner and they did not install the gas appliance correctly.

During an initial service, the customer informed FORTHRIGHT of an issue they were having, and FORTHRIGHT was able to quickly identify what the issue was and how to rectify it. It was a widespread fault which many ‘engineers’ do not grasp. 

Many heating ‘engineers’ fail to understand the underlying physics and design of boilers and central heating systems, and as a result, this leads to mistakes with the installation of boilers and central heating systems. Those mistakes develope into issues that often lead to more severe faults in time.

In this instance, the customer’s heating system was losing pressure on a regular basis in the winter and every few weeks in the summer with no signs of water leaks. The installation engineer, like many others, failed to grasp a basic concept; that water expands when heated. 

In a “sealed system,” there is nowhere for this water to expand into, so boilers that are designed for sealed systems have a built-in expansions vessels to accommodate the expansion of water when it is heated.

The total capacity of expansion that the vessel can accommodate depends on the size of the vessel and pressure. 

The bigger the central heating system, and the more towel rails and radiators you have, the more water your system will hold and the greater the expansion will be when the system is operated (heated). Higher pressures also increase the amount of expansion. Therefore, an expansion vessel should be large enough to hold the full volume of the central heating system running at its maximum temperature, and at is designed operating pressure, with all circuits open (radiators, cylinders etc).

If an expansion vessel is undersized, the pressure will rise within the central heating system and the boiler more than it should when the system is heated. If it is grossly undersized, water will leak out of the discharge pipe as a safety feature, resulting in pressure loss. Expansions vessels operating with higher volumes of water than what they were designed to do will be under higher levels of stress and wear out prematurely.

Boiler manufactures generally fit boilers with 6-10L vessels to keep boilers small and more attractive to installers/customers. Boilers that incorporate expansion vessles, such as combi and system boilers, can often eat more system water than what their internal expansion vessel can accommodate. In such an instance, an additional expansion vessel needs to be installed in the correct place, which is often specified in the manufacturers’ instructions!

Expansion vessel sizing is often not taught at colleges, nor is it part of the current heating qualification syllabus. Many ‘engineers’ are not aware of these principles, hence why a large number of ‘engineers’ do not know anything about expansion vessels. As a result, faults like this are a common occurrence. This is why FORTHRIGHT repeatedly stresses the importance of using experienced professionals as the average self-proclaimed plumber will be oblivious to such things!

Luckily in this situation, the customer called FORTHRIGHT who knew exactly what the problem was and how to deal with it. FORTHRIGHT not only repair boilers and central heating systems, we install them and inspect them, so we have a full understanding of how they work. If you are buying a new home and want to ensure you are not buying a house with hidden faults, contract FORTHRIGHT to come and inspect the heating system of the potential home prior to you buying, you will be amazed how much money we could save you!