How to change expansion vessel on combi boiler?

Combination boiler or combi boilers come being one of the most common types of boilers used in UK for a reason. Unlike the system and conventional units, the combination boilers are designed to be an all in one unit which produces hot water for taps and central heating in order to cut down the use of storage tanks or cylinders, thus occupying the least space required to house the boiler. Additionally on a comparison, the installations are much easier and faster than any other boiler unit.

The combi boilers operates by using the water from the main supply that results in stronger water pressure and ensures that you would never be lacking on hot water again. The modern highly efficient units come, being a stainless steel condensing boiler with an inbuilt heat exchanger that operates in order to serve the customers with hot water immediately.

There are two main reasons behind the combi boilers great and powerful efficiency i.e. these units have high operating efficiency and low internal water volume. This means when in summer days you don’t need space heating you are only paying to heat water which is domestically required.

Combi boilers are designed to be manufactured with two independent heat exchangers, one of which carries a pipe to the radiators while the other one carries a pipe to the hot water supply. As soon as you turn the hot tap on, your boiler fires up to heat water and a valve gets opened to let the water flow through the network of pipes.

Combi boilers are made to operate using a sealed or pressurized system because the water expands when heated and thus an expansion area needs to be incorporated into the heating system. When the heated water in the central heating system expands, it cannot be compressed and thus consequently presses against the expansion vessel’s internal membrane.

However, fitting an external expansion vessel is relatively a simple thing to do.

  1. Identify your old expansion vessel- For the first step you need to locate the expansion vessel which is usually located right next to your boiler and is connected to it. Once you are done with identifying the vessel, record the dimensions and connections in order to ensure that you get the perfect fit in the new vessels.
  2. Turn everything off- Close the shut off valve in order to turn the water supply to the heater off and the wait for some time for the system to cool down.
  3. Drain the water- Now drain out the water from the system to reduce the water pressure. This can be done by opening the bleeder valve. You are recommended to use the bucket to collect the water.
  4. Disconnect the expansion vessel- Carefully disconnect the expansion tank and keep an eye on the pipes and fittings that they do not get damaged while removing the expansion vessel.
  5. Pressurize the expansion vessel- When you turn off the water supply just make sure that the pressure reading the tank is 0. Now fill the tank with air up to 12 psi or according to the amount indicated on the manufacturer’s instructions.
  6. Check the pressure- Check the pressure in the water tank using the pressure gauge.
  7. Teflon tape- Now wrap a Teflon tape around the ends of the connectors except on the beginning of the same.
  8. Install the new vessel- Install the new vessel in the same position as the old one and carefully connect it to the heater system, however ensure the connectors are screwed on tight.
  9. Have a check- Now check the system to ensure there is no leakage.

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