The radiator cap and expansion tank cap make sure the filling hole of the radiator and expansion tank are sealed off gastight. Take the cap off and press the core of the valve, if air comes out then the expansion vessel … IRC 2009 P2903.4 Thermal expansion control. Faulty expansion vessel. This video is all about the white expansion vessel next to your unvented hot water cylinder. There is a valve on the top of the expansion vessel which looks just like the valve on a car tire. If this expansion were not possible because the water is in a closed container then the pressure rise would be an astonishing 50 bar (750 psi), this would be bad news for the pipes. This is where expansion tanks come in. Potterton Suprima 60 boiler fine after leaking expansion vessel replacement - next day cuts out before igniting. Another component which may cause your boiler to lose pressure is the expansion vessel. The purpose of an expansion tank is to provide a place for the extra or bigger water to flow, so that it does not back up out of the tank into the main municipal water supply. In this way, an expansion tank is similar to the separate radiator overflow reservoir on a car. Some expansion tanks are designed with a bladder. The expansion tank’s purpose is to protect your house’s hot water system from excessive pressure, which can cause damage to fixtures, your water heater, lines, and/or fittings. Googling revealed how a failed expansion vessel would cause the pressure to rise as the system heats up and vent through the pressure relief valve, resulting in zero pressure when next cold and failing to start. But they do a lot more than just that. Frequently it's because there is no air in the expansion vessel and this causes the system to over-pressurise and expel central heating fluid to the outside via a safety valve. A faulty expansion vessel is almost certainly causing the problem that you are describing. is it possible to remove water from an expansion tank? On a combi boiler, this component is usually fitted inside the boiler’s casing. The potable or drinking water expansion vessel. Appreciate any help. In any situation where water in a “closed system” is heated, an expansion tank is required. Pressure dropping quite frequently is usually a leak - a faulty expansion vessel has different - and very clear - symptoms. Its purpose is to accommodate the expansion of the water when it’s heated. Expansion tank problems can vary from leakage and blockage to a more serious problem that leads to a complete malfunction. Caps are designed to ensure that the prescribed pressure on the cooling system is maintained at all times during operation by allowing air to escape in case of overpressure. Listed below are a few questions answered by the Experts on issues related to expansion tank problems. Faulty expansion vessel? Expansion Vessel Problems Logic might dictate that there is a leak on your system if it pressure drops down to 0 bar often, but this is not always the case. Expansion tanks are used to absorb any excess pressure created due to thermal expansion, which prevents an over pressurization of the system. An expansion vessel When water is heated it expands, the expansion is about 2.5% from 25C to 75C. There are only two things that can go wrong with an expansion vessel and both are very easy to check - Simply remove the "dust cap" from the Scrader valve (identical to a car tyre valve) and depress the centre pin. If the vessel is faulty and the heating is say at 1 bar and the boiler heats the water in the system the pressure will increase, the expansion vessel allows the water to expand under normal conditions and so the water will stay at a pressure of perhaps 1.5 bar when the central heating is on.