Your expansion vessel has lost its pressure
What a boiler technician might say; “Your expansion vessel has lost its pressure.” What they mean: Expansion vessels are found in most boilers, especially combi boilers, and are needed to cope with the extra water created by expansion during the heating process. Expansion vessels work at pressure. If this pressure is lost, the expansion vessel cannot do its job and the boiler will fail to start or will automatically shut down.
An installer can usually tell if the expansion vessel has failed as the boiler pressure gauge will show a great increase of pressure as the boiler heats up. A faulty expansion vessel will not always need replacing – often it will simply need repressurising. Your installer will be able to tell you the most cost-effective way to fix the problem. They may recommend replacing the external expansion vessel but this can be more expensive.
Your PRV is dripping
PRV is short for ‘Pressure Release Valve.’ This is a safety device, built into a boiler that activates if the water pressure rises to a level the boiler cannot cope with. The PRV switches the flow of water to a pipe that usually discharges outside of the house. The PRV is a key safety feature of the boiler.
If you see any dripping from the PRV or discharge pipe you should contact your installer. Often they may simply have to recharge the expansion vessel. The PRV should reset and any dripping should stop once pressure returns to normal levels, but sometimes the PRV will continue to let water drip from the system. When this happens, the valve may need replacing.
You have poor flow rate from your taps
Flow rate is the term to describe the rate at which water comes out of your taps or shower. A poor flow rate means that the flow of water from some or all of your taps or shower, will be low. You can measure flow rate in litres per minute. An installer may calculate this by timing how long it takes to fill a measuring jug from a tap. Flow rate problems are typically found in open-vent systems. These systems rely on gravity to push water from a storage tank to taps and showers. The greater the vertical distance between the taps and the tanks in your loft, the better the flow rate will be. If the tank is too close to the outlet, the flow rate may be poor.
A combi boiler won’t meet your hot-water demands
A combi boiler will not be able to produce all the hot water you need. This means you will not get enough hot water out of all of your taps at the same time. You would be better suited to a system with a hot-water cylinder. Combi boilers are not necessarily suitable for every home.
If you have more than one bathroom or a large family who all need hot water at the same time, you should bear this in mind.