Lukewarm Water from Combi Boiler: Heat Exchanger

A Plate Heat Exchanger (PHE) is made of multiple plates welded together. These plates provide a greater effective surface area for the transference of thermal energy, which allows the heat exchanger to be much smaller and greater in efficiency.

A plate heat exchanger is one of those wonderful inventions that allow heat from one fluid to transfer to another fluid without direct contact. The hot liquid or "plasma" and the cold water pass through alternate separate plates and the heat energy transfers by thermal conduction from the hot plates to the cold plates, thus heating the cold water.

The hot plasma pumped through the thicker diameter pipes, heats multiple layers of brass plates very quickly. The domestic cold water flows through the thinner diameter pipe and passes through an alternate set of plates interlaced between the hot plates. The heat from the hotter plates transfers to the cooler plates thereby heating the domestic cold water supply flowing through them.

Plates can be made of brass, copper, and stainless steel. These are good conductors of heat and can withstand high temperatures.

The Plates

Here is a close up of the multiple layers of plates. The more plates a heat exchanger has the greater surface area it has to aid in the heat transfer process. PHE technology allows the heat exchanger to be small and efficient, and thereby it has become a vital component in most combination boilers.

The Capillaries

The corrugation on the plates form small capillary channels through which the water can flow. These channels are very thin and limescale can easily block them.

The chevron pattern corrugation is the most commonly used in heat exchangers because they provide the best throughput or "flow" of water and the greatest heat transference.

In a hard water area, the efficiency of the PHE can drop sharply over time as lime scale builds within its capillaries. It is therefore vital to use special descaler fluids to keep the capillaries clean and the water flow to the optimum value. It is also possible to buy descaling filters to prevent damage to the heat exchanger.

Descaler

A brand new heat exchanger will operate at optimum efficiency because all the capillary channels will be clear and open. Over time, lime scale will build up within these channels and its efficiency will drop.

A good quality boiler-descaling cleaner normally protects the internal pipes and capillaries for at least 5 years, and requires a periodic top up dose after five years. People sometimes forget the periodic top-up doses that are required. This is when lime scale begins to build up. If you have not topped up your system recently then you should get a descaling fluid.

Some of the commonly used fluids are "Fernox DS40" and "Sentinel X200". They will descale all the pipes and return your boiler to normal efficiency as when new.

These fluids are worth the money; because they cost very little and can save lots more money in the end. When your boilers efficiency returns back to as it was when new, its fuel usage will reduce thereby reducing your yearly fuel bill as well.

The great thing about these fluids is that once it is in the system you do not have to flush it out again. It stays in the system and protects it. It is a lot cheaper than having to replace a heat exchanger so buy it today and top up your system if you want to avoid large repair bills in the future.

You can find these fluids very easily and cheaply. I looked for "Fernox DS40" in Google and it came up with a dozen shops. I managed to get the heat exchanger from eBay and it was half the price compared to a shop.

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