I thought your readers may be interested to know about the real cause of this tragic accident. This is the third death in as many years.
The hot water system that has failed relates to copper hot water cylinders, the type found in most airing cupboards. When the thermostat fails to a boiler or immersion heater obviously the water can reach boiling point, if this happens the water expands quickly and enters the cold water storage tank (cistern) which is usually located in the roof space, above the airing cupboard.
However it must be noted that in the cases of the deaths the cold water tank was situated above the bathroom.
Let’s move on. When the boiling hot water enters the cold water tank it can cause the tank to flex and soften, I’m referring to a tank made of black coloured plastic, and it only happens with modern tanks made of plastic. When these tanks were first produced they were made of galvanised steel, then copper plate, then fibreglass – none of these types of tanks are are particular risk because they are rigid in fabrication.
The problem now begins to start, but only if the board that the tank is placed on does not fully support the tank. The rule is that the support board must extend on all sides of the tank by at least 150mm ( 6″ ), which will provide adequate support. If the support is not present the tank can soften and split and out comes the boiling hot water.
If the tank has been replaced and the original tank was one of the rigid types there is a chance that the fitter (plumber) has used the same board, but it’s not big enough for the new tank. Most modern tanks hold more water and are thus biggger than the previous types....
However just because the thermostat fails it does not mean to say that this sequence of events will happen, generally the system just shuts down.
What should owners of property do? First of all check to see if you have a copper cylinder in the airing cupboard, secondly get into the roof space (or wherever the cold water supply tank is situated) and check the size of board supporting the tank. It should also be noted that this board needs to be at least 18mm thick, preferably made of plywood. If the board is not the right size, and you feel confident enough to drain down the system, you can replace the board yourself, if not then obviously you can call in a qualified plumber. You could also get the thermostats checked out by an electrician, but to be honest they could be tested today and fail tomorrow.
Whilst writing if any of you out there, or one of your staff, are looking for plumbing qualifications, our college is available for advice and training to City & Guilds standards.
John Smith R.P., A.M.I.P.H.E.