Immersion heater tragedy

[Flyfisher]

For the neurotic, fit an external thermostat on the tank (removing any insulation first).............

They're liable to fall off, or someone will fiddle with the settings.

Probably easier to fit such a device to the hot water pipe exiting the tank as this would avoid the need to remove any insulation.

We have an external thermostat fitted to the hot water pipe on our Rayburn. It's clamped to the pipe and I can't see how it would fall off (without tampering). It also has a max temp setting of 90C making it fiddle-proof in terms of detecting boiling water.

In our system the pipe thermostat is linked to the central heating pump and overrides the timer settings forcing excess hot water (in this case from the Rayburn) to be diverted to the radiators.

 

[Penners]

The latest problem we have is that when the heating comes on, red hot water splurts out of the overflow pipe onto a porch roof then onto the lawn. Not ideal and I am not sure what to do.

Marm, that sounds as though it could be a manifestation of the same problem that I mentioned at the start of this thread. The overflow pipe could be serving the header tank, meaning that hot water is venting up into the header tank.

You really should get it looked at as soon as possible. If the header tank were to fail because of the heat, you could have hot water cascading down through the house.

Of course, it may be something else altogether, but honestly - you need to know.

 

[Schoolmarm]

I have got a new plastic cold water tank supplying the cold taps and a header tank for the central heating also new plastic.

I had it fitted with a new ballcock a couple of years ago when it was doing the splurting thing before.

It doesn't splurt if just the immersion is on, it only does it when the central heating boiler comes on.

I will get a plumber contacted ASAP.

 

[Penners]

I have got a new plastic cold water tank supplying the cold taps and a header tank for the central heating also new plastic.

I had it fitted with a new ballcock a couple of years ago when it was doing the splurting thing before.

It doesn't splurt if just the immersion is on, it only does it when the central heating boiler comes on.

I will get a plumber contacted ASAP.

OK, the hot splurting (I'm glad you use the correct technical terminology) is almost certainly nothing to do with the ballcock, which just allows cold water into the tank if its water level drops.

It will probably be hot water that has risen up the vent pipe from the storage cylinder, because it's getting too hot. If it doesn't happen when only the immersion heater is doing the heating, then I must assume that it's your primary (ie: central heating) circuit that is getting overheated.

What heats your water? Is it something like an Aga, or similar? If so, I wonder whether the "heat leakage" radiator has been turned off, or is clogged up. Or perhaps a thermostat in the boiler or on the cylinder has failed.

In any event, hot water spilling out of an overflow is something that you certainly shouldn't ignore, so your plan to get a plumber in ASAP is well worthwhile.

 

[Schoolmarm]

It is heated by an oil fired boiler, we had it installed about 6 years go.

I have it serviced every year.

I think you are right about it being the boiler because now I think about it, the splurting doesn't happen if I have the boiler on a lower setting.

 

[chuckey]

Schoolmarm, if you start with your heating off the level of water in your header tank is set by the ball valve (this level is also in the boiler vent pipe as well). when the boiler fires up the water gets hot and expands and the level in the header tank rises, and in your case over flows. The easiest solution is to re-adjust the ball valve to set the header tank water level to the very lowest possible. Its purpose is to initialy fill the HW system and to make up for loss by evaporation.
Frank

 

[Schoolmarm]

Ah, thankyou for that. I did fiddle about with the old one but have left the new one alone.

 

[Penners]

Schoolmarm, if you start with your heating off the level of water in your header tank is set by the ball valve (this level is also in the boiler vent pipe as well). when the boiler fires up the water gets hot and expands and the level in the header tank rises, and in your case over flows. The easiest solution is to re-adjust the ball valve to set the header tank water level to the very lowest possible. Its purpose is to initialy fill the HW system and to make up for loss by evaporation.Frank

But Frank, Schoolmarm says that the water coming out of the overflow is "red hot". To me that indicates that the hot water in the vent pipe is rising up and flowing into the header tank, which (a) isn't right, and (b) could be dangerous.

 

[Schoolmarm]

Aww bugger. Right I am leaving well alone and ringing a plumber tomorrow.

 

[mrssmith]

Hi there, I am reading this thread and getting very confused (which doesn't take much!). I am worried as we have a solid fuel rayburn heating our water where the tank is in a cupboard in our sons bedroom, he is two and about to be joined by a new baby brother/sister in 2 months. The thought of the tank exploding fills me with absolute horror.

We have one radiator from the rayburn which I have been told is there to cool the water. There seems to be no water tank in the attic. Does this sound like a safe system?

Just before we bought the house two years ago the previous owner had just replaced either the thermostat with the tank or just the thermostat. Should we get anyone one to check it out?

Many thanks
Charlotte

 

[Penners]

Charlotte

Firstly, we're talking about a very rare occurrence under a certain set of circumstances, so don't lose any sleep.

The event that was recently reported in the papers did not involve the hot water tank exploding. It was a faulty immersion heater that - due to the way the plumbing system was designed - sent boiling hot water up into the attic, and into a plastic storage tank, which collapsed due to the heat.

If you have a hot water cylinder in a cupboard next to your son's bedroom, and no header tank in the attic, then I suspect you may have a cylinder that has an integral header tank immediately above it. In which case the header tank is probably copper, and so won't be melted by hot water.

If your water is heated by a solid fuel Rayburn, and has a "heat leakage" radiator, then everything should be fine. Just make sure that this radiator is never turned off at a time when the Rayburn is generating plenty of heat.

 

[Aidan]

We have one radiator from the rayburn which I have been told is there to cool the water. There seems to be no water tank in the attic. Does this sound like a safe system?

Just before we bought the house two years ago the previous owner had just replaced either the thermostat with the tank or just the thermostat. Should we get anyone one to check it out?

Many thanks
Charlotte

1) There should be a feed and expansion (F&E) cistern. These are usually of 4 gallons capacity (typically 18" x 12" x 12") and are usually in the loft. It may be in the top of the airing cupboard.
This tank contains the gungy boiler water which will contain chemical corrosion inhibitors. rust, limescale, etc.). They should be set up so that the water level is about 2" above the outlet. The boiler/Rayburn water expands into the F&E tank as it heats up.

If you can't find one, them I'd get the system checked out and I would not use it until it had been given the all clear.

2) There is usually a cold water storage tank in the loft as well; these can be of any capacity to suit the number of occupants, but domestic ones are typically 50 gallons (about 48" x 24" x 24" ). They can be round or rectangular. These store the water that you use for bathing and laundry. The water in it should be clean, but I've seen some filthy ones in some lofts.
They look like these;

http://www.screwfix.com/prods/10134/Plumbing/Cold-Water-Loft-Tanks/Cold-Water-Tank-50gal-1175-x-596-x-506mm

You can have mains-fed systems ( which have no tanks) with an unvented hot water storage system; however you cannot have an unvented hot water storage system with a solid fuel boiler.

So, the answer is that you should have two tanks in your loft, a big one and a little one. If you haven't, get a plumber in.

The technician/plumber should be HETAS registered to work on solid fuel boilers. There's a list here;
http://www.hetas.co.uk/pdfs/CPRS_index.pdf

Your neighbours would probably know a local plumber who could do a check.

The chances of a properly installed vented system causing an explosion or causing an accident, like those reported recently, are minute. They're about the safest system you could devise.

 

[Aidan]

It was a faulty immersion heater that - due to the way the plumbing system was designed - sent boiling hot water up into the attic, and into a plastic storage tank, which collapsed due to the heat.

Perfectly true, but a modern plastic tank would tolerate boiling water. The accident last year involved a 30 year old tank, the 2002 accident involved a tank that was not properly installed and was overhanging its base by 8". See http://www.iphe.org.uk/databyte/tank_cistern_installation.pdf

Both accidents would have been avoided if a modern manual-reset immersion heater thermostat (£4.50 ish) had been installed.

You'd usually hear the water boiling in the cylinder.

I used to have a solid-fuel boiler in a workshop, in which I burnt wood offcuts to generate hot water. It boiled regularly, with no adverse effects on the plastic F&E tank.

 

[mrssmith]

Thank you for the advice and reassurance. I think we need to have a thorough poke around in the attic, my husband thought there was no tank up there but we will check again. I think we will get it all checked out anyway for peace of mind particularly as the pipes have so many air locks in, every couple of days we have to switch the water off and switch on the taps to drain it.

There were an awful lot of shortcuts made by the previous owner so anything could have been done with the system, but thank you, I do feel more reassured.

Charlotte

 

[MdB]

Another option is like our system (not that I recommend it).

We have Rayburn which is directly linked to the hot water tank. i.e. the water from the hot water tank comes down into the Rayburn to be heated and then returns to the hot water tank. As the hotwater tank is vented there is no danger of explosion though as there is no thermostat, the water can get very hot. I wasn't very happy with this and wasn't too upset when the oil tank feeding the Rayburn split and knocked out the system. We now just use electricity to heat the water which we think is slightly cheaper.

We also don't have a cold water tank which is direct fed to the taps.

 

[Cloudscape]

If you have a header tank that feeds the hot water tank... you can usually hear it. Run off some hot water and then turn the tap off. You should be able to hear water running through the pipes to fill the header tank.