Wednesday, January 09, 2008

Inside information

As I am a) a bit geeky and b) a bit anxious, I read P&HE Magazine from cover to cover. It's more interesting than you might think. No really, it is.

So I knew about this baby scalding case a while ago. The mainstream reporting on it is a bit wonky, which is understandable, as what happened (or at least what the plumbing industry body thinks happened) is a little complex to explain.

But let me try, in case you have a water storage cistern in your loft and a small child (or a large child, or yourself) in a bedroom under it and this story has worried you.

The water was not heated in the loft, but, like most stored hot water, in a hot water cylinder, probably in an airing cupboard. Most hot water cylinders have two ways of heating the water. The main way is via a coil, which circulates hot water from the gas boiler, but for back up or top up there is an immersion heater, which is powered by electricity and works much like a kettle element. You turn on the immersion heater and the water heats up until it reaches a certain temperature, when the thermostat turns it off.

If there is no gas then there might just be an immersion heater. This is a pretty expensive way to heat water, especially if the cylinder isn't well insulated, but it does happen quite a lot.

Cylinders heated in either of these ways are vented. As the water heats, it expands, and there is a pipe up into the loft space to allow for expansion. This ends over a cold water storage cistern (tank). This cistern generally stores water for the cold taps, though these can also be fed directly from the mains, and also feeds cold water into the hot water cylinder as hot water is drawn off via the hot taps. If steam rises up the pipe, it will condense and drip into the cold water cistern. But cold water is being replaced all the time as hot or cold water is used, so that water should stay pretty cold.

Unless the immersion heater is on and the thermostat fails. In which case, over time, that water will get hotter and hotter. The water in the cylinder will boil, go up the vent pipe, condense into the cistern, more water will be drawn into the cylinder from the cistern, and it will go round and round. In extreme circumstances, if no water is drawn off (which would bring cold water into the cistern from the mains), the whole system could reach scalding temperature.

Which is obviously potentially lethal. *However* even if that happened, if your storage cistern is compliant with the Water Regulations, which stipulate what material it should be made out of, what type and size of platform it should be sitting on, and what kind of covering it should have, then it should not fail in the way that this one did. This one was apparently on too small a platform, and was overlapping its edges. This doesn't matter if it's not hot, but once the water heated up, the plastic warped and the whole thing flipped, with dreadful consequences for the baby sleeping underneath it.

So, brothers and sisters. Don't ignore a dodgy thermostat, is the easiest thing to do. And make sure your plumber isn't like some of the guys on my course, who didn't write their names on the front of their copies of the Water Regs to make it easier to sell them on when the course was finished. You know, like doctors sell their anatomy books. They'll never need *them* again, right?

Just felt I needed to say that.




Blogger bedshaped said...

It's annoying for me, to say the least, when I tell people about this potential problem when I see what terrible state their current storage tank is in. I've seen some crap set-ups. The sad thing is, when I give people my advice, they are ALWAYS swung by the financial factor. Obviously, a new storage tank, connections and labour is gonna cost them money and they always, ALWAYS think I'm just out to make another few quid. No matter how genuinely concerned and sincere I am.
I've got my Water Regs and have been told many times that in certain situations, I have the authority to 'condem' something, particularly if it poses a potential danger. I've never used that authority, mainly because, again I think people would see it as me 'trying it on'. I'm finding it a bit of a catch 22.

11:07 pm  
Blogger Jo said...

Have you tried waving your Water Regs around a bit? But I am still inxperienced at these things. The only CWSC I've actually changed had a dead bat in it, mind.

9:30 pm  

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