New Electric Immersion Heater - but only 4" of hot water in bath

[greenprodrive]

Guys

In response to my central heating bioler failing (long story , £3k quote from plumber, and I can't afford it due to recession).. I have had a 27" electric immersion heater element installed in the upstairs36" hot water cylinder.

Works of it's own switch. Three times now have tried having it on for in excess of 3 hours each time, and each time only get approx 4 inches of water in the bath tub.
Is this normal ?

I've stuck my ear to the tank and can hear it faintly working (which it does for the entire 3 hours) [I know its the heater element becasue when I turn it off the sound goes away)

It has it's own thermostat set at 65degrees (and this hasn't triggered by the way) , so it all points to the element "working" , and yes the first few inches of bath water are hot, and then it goes col.

When it worked off the boiler, the bath water would (of course) heat up quicker, due to it being the bolier that did the heating, but also , much more hot water.

I'm stumped. Could it in some way rely on any of the pump/valves/domestic circulator stuff that were all "on" when the boiler was working ? [The plumber turned them all off]

Any help - much appreciated

 

[PlumbBobBob]

the immersion will only heat the water in the top of the tank whereas the coil in the tank heated by the boiler is lower down in the tank and heats all the water lower down as well. as you know heat rises, with the coil lower it creates circulation in the tank and so heats more water.

 

[Dannypipe]

Are you certain that the immersion is the correct length. You can get them as short as 11". Which for a top entry immersion heater is useless.

 

[easyt]

I have a very large cylinder but 30 mins and enough water for a full bath.

 

[justlead1]

Hi have a look at the electricmeter whilst heater is turned on. 3 Kw an hour will be used if is working correctly, if not heating where the power going?

 

[Puddle]

27:immersion heater correct size and will heat a full 36*18 cylinder in 1 1/2 hrs ish,you have a faulty immersion heater or built in thermostat

Get the fitter back to sort if just fitted

imho

 

[wnjswozo]

stat on immersion set to low

 

[tamz]

Theoretically assuming.
117 litre cylinder
immersion stat set to 65°C
cold water temp 12°C
Using a 3kw immersion it would take 2hrs 24 minutes to heat the tank of water.
I hr would give you approx 48 litres @65°C.

A std bath holds 200 - 230 litres to overflow level (say 230) and if you weigh around 13st (80kg) you will displace 80 litres of water (if you lay under the water).
So you need 150 litres of water @ 42°C to have a full bath.
This would need approx 85 litres of hot @ 65° which would mean you need to turn the immersion on 1hr 45minutes before you run a bath.
If the wife is just a wee thing and weighs 50kg she would need 180 litres of mixed which would mean she would need the full tank and you had better leave the immersion on as she will be in there for ages topping it up.

Get yourself a shower fitted.

easyt
big immersion or shallow bath

 

[easyt]

Look at it another way Tamz. Assume your 150 litres is correct. Then, for me, a hot bath is blood temp. 37C. 42 ok for a hand was but not for my total immersion to raise water temp by 25c = 25x150 (litres) x 1000= 3,750,000 cal

At this point I need conversion tables They say 4.36 kw hours required. say 11/2 hour. Well spotted that man Tamz

I suppose that when I used to use immersion heater for a bath (10 years ago when central heating boiler was due for replacement) it was probably on for 30 to 45 mins. My mistake is that the water in the cylinder would have already been warm. It would have been heated in the morning, Probably boosted teatime and still fairly warm before heating for a bath at night.

This Summer when I had my old heating oil tank removed and until I ripped the bath out we were mainly showering. After the bathroom was refitted and whilst I was constructing new base, plinth and fire wall for new oil tank we were showering and so not using as much water.

Normal bath Tamz, 3KW immersion I suspect, lousy logic

 

[tamz]

The easy way to count it is

volume of water x 1.16 (constant) x delta T = watthrs
The 1.16 is the amount of energy required to raise the temperature of water by 1°C in watts.

eg
150litres x 1.16w x 25°C = 4350watts (4.35kw)

If you like to work in old money
say
30gallon x 10btu x 77°F = 23100Btu

The 10 is a constant as it is the amount of energy in btu to raise the temp of 1 gallon of water by 1°F

 

[easyt]

If the OP's element is actually heating for 3 hours an big enough tank then he should scrape two decent baths out of it (not full to the gunnels) don't you think Tamz?

 

[REDSAW]

ithink tamz is stuck at home too much in this snow.
very interesting tho' lol.

 

[tamz]

What happens in reality is the thermostat will switch off and on a few times as the cylinder heats to set temp of 65° and the water in the tank will be layered at different temperatures.
So although in theory it would take 2hrs 24 minutes to heat the full tank to 65° from cold, in reality the top 18" (the thermostat is only 18" long) will be around 65 and the rest will be progressively cooler.
There is an idea! Wrong length thermostat??

You are correct in that most times the immersion is not heating from cold. There will be some hw already there so the times should be lower.

2 baths for the weans.

You are right Redsaw. Starting to go stir crazy.

This week has been a nightmare. Over 3ft of snow. But it has been stopped since this afternoon. Temps plummeted to minus 16 -17 tonight. Probably lower before morning. Worst start to the winter i have ever known.
Done a couple of wee things myself and one of the lads has managed to get to Falkirk every day except Monday so at least there is a bit of money coming in. The other 2 have been in the pub for 4 days! and getting paid for it!!
Most of the work involves an hour or so travel each way which in these conditions means 3-4hrs so it is a no go. Merchants couldn't even get the stuff out!
It just means i have a hectic few weeks rescheduling stuff.
Such is life

 

[easyt]

Sorrry you are under siege Tamz. I live near Chester and I suspect we have had an inch of snow in total. Only -10c this morning. Reckon you will be stranded a while longer.