immersion heating woes...

[Russ]

.and the next thing to go wrong in the house is.......

the immersion heater

Ok, full story, so any clever heating engineers can have a think will the full picture.

About a month or so ago, we got a monster electricity bill for the year (12 months at =A330 a month, then an additional final settlment bill for another =A3312). Electricity company never sent us any bills all year, so didnt' realise how much we were using....anyway, that's another story.

Investigate the big electricity guzzling devices, starting with the water tank immersion heater.

Turns out the timer is burnt out...completely, so the immersion heater has been on for a whole year 24/7 although there is a thermostat in there...but don't know if that was working properly or not (it was set to about 75 degrees Celcius). Insulation on all the wires going into and out of the timer had burnt off/melted and there were black burn marks on the wall too where it had been.

Bought and fitted a new timer device, which works fine now.

However, since replacing the timer there doesn't appear to be as much hot water as there was before - as you can barely have enough for 2 people to have showers before the water starts coming through the shower cooler and cooler.

The immersion heater is currently set to come on at about 4:00am and go off at 8:30am - so that's a good 2.5 hrs before I use the shower at

6:30am.

I've replaced the thermostat (because the temp adjusting knob snapped off the old one), and the new one has a thermal safety cut out thing, so if the water gets too hot it will shut off (but you can reset it).

I tried having the thermostat turned up to about 70 degrees (as it was before I changed the timer) but the thermostat kept tripping, so I've gradually been turning it down and down (think it's not at about 60 deg and it hasn't tripped yet).

There's still hot water out the top of the tank going to hot water taps, etc - and this water is still plenty hot enough to cause an 'ouch' if you have your hand under it too long!

I think the immersion heater is a 27" one, as it has an 18" thermostat.

Here's pretty much how the hot water tank is (kind of to scale to in terms of heater and tank outlets):

can feel the shower feed pipe is hot, but then it obviously gets colder as the water is used.

I'm in the shower for literally 5 mins (10 max), and my wife then uses it after me for about 10 mins (15 max).

So not exactly running the shower forever.

I've got a new immersion heater (27" again, as the guy said that was the largest that would fit in a tank or that size) and I'm hoping that the problem is because the end of the immersion heater is either damaged or the whole thing is calcified.

Just seems really weird how we never had shower hot water shortage problems when the thing was apparently buggered - yet now with new thermostat and timer it seems to be crap?

The only thing I can think of is that the heater was literally boiling the water so that when cold water comes into the tank, it gets heated by the already raosting water not only the heater. If this is the case, I need to find a thermostat that will allow the heater to really heat things again, so that the shower then uses less hot water to mix with the cold (it's a thermostatic mixer valve on the pumped shower, by the way).

Any advice or opinions would be most welcome!

[Sadly]

Two comments:

1) Re-routing the shower output to run from a Surrey Flange (at the top of the tank) would make a huge difference.

2) If the only option you have for heating water is electricity (and especially if most of your hot water is used for showers) it would seem to be far more economical to have an electric shower and run the immersion for only an hour or two a day, set to a much lower temperature.

[Russ]

The Surrey flange has been mentioned to me by another guy elswehere, but I'm not sure how to fit it, as I don't rally have much /any plumbing experience apart from fitting new taps, etc!

[Harry Bloomfield]

Russ presented the following explanation :

Water temperature in a tank will be stratified. Only the water above the bottom of the water heater will normally be warmed and as it is used up it will be replaced by cold at the bottom, so the hot/cold interface level will move up. If your diagram is to scale, the shower take off is not much higher than the lower tip of the element, so not much hot water available to be drawn before it runs cold.

[Russ]

Upon having a closer look at things now I've got home, the 27" immersion heater goes a LOT further into the tank than my guessed sketch above. THe shower outlet is only about 1/3 of the way down the immersion heater, so should be plenty of hot water.

Just tried to remove the old heater, as I got a new one at lunch. It's not budging at all.......not an iota. I've bent the immersion heater ring spanner and even some stilsons as long as my arm couldn't persuade it to move.

Actually looks like someone tried removing it in the past, as there are scratch marks where an immersion spanner could have slipped off the heater nut. I reckon someone else had a go and gave up.

Bottom line is I think we need a new tank. The heater's probably f*cked and won't come out because it's calcified in place. WHich might explain why the previous owner left the heater on 24/7 because it's caked in limescale and takes forever to heat all the water in the tank properly.

Anyone reommend a good plumber in my area?

[Harry Bloomfield]

Russ wrote on 04/01/2006 :

The hottest water will still be at the very top of the tank.

Calcification can quickly lead to the element over heating and burning out. You might try tightening it a little before trying to undo it and as you have nothing to loose - try draining it down and applying some heat from a blow lamp of heat gun. If its an old tank with a retro fitted immersion boss, it will have been drilled out and a boss plumbed into place. Heat would certainly get that out complete with the boss.

Plumbing a boss in takes a little practise, but is quite satisfying :-)

[Russ]

I think it's new tank time, as the tank looks like it's been there forever - as does it's immersion heater!

Can anyone recommend a plumber in the Weybridge/Surrey area? I don't fancy getting ripped off by a randomly selected guy from Yellow Pages.

I think the tank I need is approx =A3200, the immersion heaters are only =A315, so it should be a fairly straight forward swap, with just some minor modifications to the pipework for the inlets and outlets to meet the new points on the tank?

Roughly how much should I be looking at for getting this done (so I know if quotes I get are in the right ballpark!)?

Cheers

[meow2222]

You've got this all wrong, and are now in the ass over barrel position, ready to give your money away for no reason.

Your immersion heater works perfectly, that much we know. The tank is watertight and does everything it needs to do. The plumbing setup is also fine, since it all worked fine until recently.

The problem is with the thermostat. Old stats could be set anywhere upto around 95C, and you'd set it to give as long a showering time as you need. New stats are required to have cutoffs at relatively low temp, i forget exactly but something like 65C, which is fine for a lot of systems, but totally inadequate for some. The solution is to use a separate strap on thermostat with your existing element, a stat that you can set to whatevers needed. Screwfix do one, cost about =A38.

NT