4) Immersion heaters - DANGER FROM BOILING WATER IN LOFT TANK slight error I think!

[ericmark]

I was reading the thread on frequent asked questions, and I do remember the death of the baby due to the header tank failing. As where the only heating of the water is electric with a single thermostat what has been said is correct.

However where other methods are also used to heat the domestic hot water, especially solid fuel although it would also apply with twin electric thermostats then a fault with the alternative form of heating can and does cause the electric back up to fail, and the over heat sensor needs to have a manual reset.

In the old days of having a side boiler on our stove, it was common to hear the water boiling, and we would have to run off some hot water, with solid fuel the header tank is not made from thermal plastic, it may be plastic, but not the type which loses it's form when it gets hot. So the tank can be full of boiling water without the danger of it failing, in the main the header tank is steel.

After the stove had cooled to use the electric immersion heater (fitted 1954) we would need to go up and press the large red reset button, all British thermostats had the reset button, it was only the cheap imports which lacked the emergency cut out.

In the main gas never boils the water, nor does electric, so having a non resettable cut out is normally not a problem, but clearly if the off peak immersion heater thermostat fails then it will trigger both the off peak and the emergency second thermostat allowing one to heat the water if off peak fails, and visa versa so with more than one heating method the cut out needs to be resettable.

The cure would be to ban thermal plastic header tanks, the non resettable cut out was a cheap fix until a better fix could be found, the worry is should a thermostat fail once, it is likely to fail again, so the non resettable cut out ensures the thermostat is changed. However this is only valid when there is only one thermostat controlling the domestic hot water, with two or more thermostats then only way to ensure the back up does not fail erroneously is to use resettable types.

And old way to stop a thermal plastic header tank failing is ban thermal plastic header tanks.

 

[mogget]

A thermoplastic header tank if made to the right standard, should be able to contain hot water, if supported adequately across its base and 150mm all round. This is regulation, as is the need for a over temp immersion cut out.

I'd be interested to hear whether there have been any similar failures to the case at hand, in a system that had been installed to current regs.

If there's a failure of a system due to being inadequately installed that's not a problem of the regulations, it's the fact that someone did a bodge job.

Water and gas regs apply to everyone, not just professionals.

 

[ericmark]

I have no problem was an over temperature thermal cut out, they have been used as far back as I can remember, the objection is to non resettable thermal cut outs where there are more than one method of heating the water.

I have seen plastic tanks made of a type of plastic unaffected by 100°C clearly you don't want steam in the loft or boiling water running out of an over flow, and there needs to be some thing to stop it over heating in an unattended property.

However I know full well the noise produced when the water boils in the pipes alerts one to something being very wrong well before any cold water tank gets hot enough to split, as a child I heard it many times, and my mother would send me to run off some hot water, mainly happened when she was baking and the stove what cranked up a bit.

And once cooled the red reset button would need to be pressed before the immersion heater could be used. In fact when we wanted to use the immersion heater we always pressed the red button as at some time between each use it was likely the coke fired stove had caused the water to boil.

 

[Grumpy Gasman]

The open safety vent should terminate to drain via a tundish situated above the level of the CWSC.

 

[ericmark]

The open safety vent should terminate to drain via a tundish situated above the level of the CWSC.

The tundish should also be glued, failure to glue the tundish was one of the reasons for the death of Emma Shaw however the blame was assigned to an electrical foreman for using unskilled labour.

 

[Grumpy Gasman]

The tundish should also be glued

Copper tundish would be soldered.

 

[ericmark]

Agreed but in the death linked the tundish should have been glued. In that case so many people made errors.
1) Seems the electrician had left a little extra cable which had looped so not all within the safe zone.
2) Clearly the plaster had hit the cable, as to if he could have known is unclear.
3) Either when plaster hit it or when power turned on there would have been a bang when the earth cable cleared its self, this was clearly ignored.
4) As said there should have been a cut out to stop water over heating.
5) As said the tundish should have been glued.
6) The stop cock should have been bonded.
7) The electricians mate should have written down actual reading even if OL and not fudged up a reading asking lads in canteen.
8) It should it seems from court case have been an electrician taking the readings.

And to be frank most accidents are not due to a single error, but a whole load of errors which together allowed it to happen. And often we simply don't recognise the warning signs. I walked pass my caravan couple of years ago and the smell was rotten, however it was parked over a drain, so did not immediately realise what was going on. However then I realised it was the smell of a battery being over charged, a cell had gone short circuit.

Be it the sound of water boiling or smell of caravan battery we can simply not recognise what it means.

However where we have other methods of heating the domestic hot water to electric, the immersion heater is often just a back up. And to have it so a fault on the main method of heating domestic water can result in the back up also failing is clearly wrong.