Immersion boiler not heating water hot enough.

Chrysalis

So in my home I have an immersion boiler, I believe its only a single element at the top and thermostat at the top..

I used it when I first moved in a few times but found that the water was nowhere near hot enough for a bath, and just about hot enough for washing dishes, but dishes had to be washed right away, as it was only just about hot enough for immediate use.

I then switched to using gas boiler for water heating, the water from that was steaming hot which is what I wanted, and could fill entire bath with it (mixed with some cold water), and hot enough to use in sink with letting pots soak and still hot enough an hour or so later to wash them.

Now my gas boiler is out of use due to failing a safety check, its still unknown what is happening with that so I started using the immersion again.

It turns out the thermostat failed on the immersion, so the first time I used it, it over heated the water, but I resolved it and the bath was fine.

I then used it a second time, but this time with timer set on my phone for 15 minutes sooner than when it started boiling the first time, no over heating, nice steaming hot water.

Now a new thermostat has been fitted, it was set to 60C by the person fitting it, he insisted 70C would be way too hot, and it is back to being nowhere near hot enough, I can see from the smart meter data, its only done about 40% of the heating before thermostat cutting it off.  I ran it for the same period of time as the second run.  But it had auto cutoff about 25 minutes before that.  Basically the hot water coming out is hot to the touch but not hot enough to make you pull finger away, for use of the bath, it needs to be hotter as to fill the bath I have to mix cold water with it, as if I try to fill with just hot water when the bath is only half full it turns cold.  I dont have this issue with the gas boiler, and I didnt have that issue when was no thermostat.

I did some reading and apparently I might be suffering from only the top part of the tank heating up, there definitely is no bottom element or no bottom thermostat as I was told whilst the thermostat was being replaced, and I dont see any cover or anything indicating that, just at the top.  Also only a single element, I did see the element briefly when it was being fitted, it was long'ish, but if I am remembering right definitely not long enough to go right to bottom.

Albermarle

You seem used to having pretty hot water. At 70 in the tank it could potentially scald someone as it comes out of the taps. On the other hand 60 is maybe a bit on the low side, especially if you have a long run from the tank to the taps.. and you like your water hot. Can it be adjusted to 65 maybe.

Rodders53

The tank immersion you have is a backup emergency for while the boiler is fixed. Due to the thermostat location you will probably never get a full tank --- but try leaving the immersion on for a long time to see if that helps heat a larger volume of water. 
Even left on 24/7 the thermostat will only operate to keep the water at the pre-set temperature.

Ditto but after setting the thermostat to 70 C (or whatever the max is) but be very wary - even 60 C can scald the skin.
Current building and water regs require thermostatic mixer taps to baths to reduce the risk!

Check what the tank thermostat for the boiler hot water is set to?  It may well be that it was set high and the boiler water likewise (and a less economic way to run - but that's for another day).

You were probably heating the water to a dangerous 90-100 C temperature when the thermostat failed .

Get that gas boiler sorted asap. 
Winter is fast approaching and tradespeople will be inundated (and more expensive).
It's also 1/4 of the cost to heat water via gas than using electricity.

Chase your Landlord if you aren't the Owner.

EssexHebridean

You should be able to isolate the tank electrical feed, then remove the cap from the thermostat and alter the set temperature there. I’d agree that 70° is probably too high for safety - it maybe that you can toe rate it but anyone visiting who used water could be scalded. 65° and a warning to visitors that “watch the hot water, I have it set a bit higher than normal” could be a compromise. 

Google search for “adjusting temperature on immersion tank thermostat” and you should find some YouTube videos to give you a clue. 

Chrysalis

Albermarle said:

You seem used to having pretty hot water. At 70 in the tank it could potentially scald someone as it comes out of the taps. On the other hand 60 is maybe a bit on the low side, especially if you have a long run from the tank to the taps.. and you like your water hot. Can it be adjusted to 65 maybe.

So you think a 10C adjustment is a very big one?  It can be put on 65C yeah.

I think the average temperature might be a lot lower though, as I think there is cold water at the bottom of the tank and the thermostat is just measuring the hotter top part.

Also the immersion might become permanent for my hot water, there is no assurance I am getting a replacement boiler, its out of my hands as I dont own the property.

The problem is if the water is only warm, it wont be enough for a bath, the bath can only be filled hot when the hot water is a bit too hot for comfort, and then cold water top up makes it comfortable, and that cold water is enough to fill the bath.  The gas boiler also was pretty hot water.  I think there should at least be a little steam when filling a hot bath.

If the water cannot be hot enough for that, then I expect I need a new tank at least twice as big and heated from top to bottom to be adequate.

Mutton_Geoff

The thermostat looks something like this. The rotary dial for setting temperature should be visible through a small hole in the cover (near where the cable goes in).

EssexHebridean

The immersion may be the least of your problems here if you do not get the boiler replaced - how is your home heated? If it is designed to be on gas central heating, then be warned that to heat to the same level using electric heaters of a plug in type will cost you a fortune. I would lean on the landlord to ensure the boiler gets sorted ASAP if I were you! 

FreeBear

EssexHebridean said:

The immersion may be the least of your problems here if you do not get the boiler replaced - how is your home heated? If it is designed to be on gas central heating, then be warned that to heat to the same level using electric heaters of a plug in type will cost you a fortune. I would lean on the landlord to ensure the boiler gets sorted ASAP if I were you! 

Electric heating, if using a heat pump that has been properly specified and configured, can be as cheap as gas to run. During the summer months, it could even work out cheaper. Any other form of electric heating, I would agree, will be darned expensive to use.

Having a gas boiler already means that you (or rather the LL) qualifies for a Boiler Upgrade Scheme (assuming you're in England or Wales). This is worth £7500 off the cost of installing a heat pump and may well bring the price down to below that of a replacement gas boiler - Have heard Octopus quoting well under £2K for an ASHP (under £1K in one case). They quoted me around £2700 earlier in the year..

Perhaps worth having a chat with your landlord - Having an ASHP would mean that he/she wouldn't have to get a Gas Safe certificate every year for the boiler. Could also add value to the property.

nofoollikeold

1. As others have said, heating with gas is much cheaper than with electricity, even with economy rate electricity.
2. However, it is possible that the immersion heater itself, or the thermostat, is the wrong length.
3. The immersion heater, if fitted at the top, should be almost as long as the hot water cylinder is tall, bar about 4 to 6 inches.  If it is significantly shorter, it will only be heating the water in the top part of the cylinder.  
4. The thermostat normally fits inside a sealed tube, and should be almost as long as the immersion heater itself, again bar a few inches.  If it is significantly shorter, it will shut off the electricity to the heater as soon as the water at the bottom of its length reaches the set temperature, leaving water below much less heated.  
5. If it is a rented property, as others have said, it is for the landlord to sort out.
6. If it is your own property you will have to sort the problem out.
7. If you are confident, experienced enough and competent to work with potentially lethal mains voltages you could try the following:
7.1 Turn off all electricity to the property at the consumer unit and at the immersion heater switch.
7.2 Remove the cap from the immersion heater.
7.3 Undo the electrical connections to the thermostat and withdraw it.
7.4 Push a piece of stiff wire down the thermostat pocket until it reaches the bottom.  
7.5 Withdraw the wire and measure it.
7.6 If the measured length is within about 8 inches of the height of the cylinder, the immersion element is the right length.  If it is much shorter than the cylinder is high, a new complete immersion heater and thermostat is needed.  I would suggest this is a job for a plumber, as they are often difficult to remove.  
7.7 If the immersion is the right length and the measured length of wire is roughly the same length as the thermostat part that fits in the pocket, the thermostat is the right length.  If much shorter, then a new, correct length, thermostat is needed.  Subject to your confidence and competence, this is an easy DIY job.  

Kiran

So you are heating water in a cylinder with the immersion. The cylinder will also have  high limit stat that shuts off the power to the tank if the temperature is reached. These are designed to stop the cylinder exploding in the event that water starts turning to steam. Check what that is set to and don't set the immersion higher than that. I'm assuming that your boilers heat input coil is lower than the immersion element? That will be heating the tank volume by cavitation. Im guessing if the immersion is higher then the heat is only being applied to the top of the tank and it takes a lot longer for the temperature to equalise. Do you get a short burst of hot water followed by cooler water? .It is definitely possible, as suggested above that he wrong element has been installed so that would be worth checking too 

Chrysalis

I have tried it at 70C now, its a bit better, but not good enough for bath use, still not hot enough for any steam at all, its true I couldnt keep my hand under the water when it first started coming out of the tap although no risk to scolding myself, but it didnt take long for it to drop temperature, the main difference is I could fill the bath to about 2/3 instead of 1/2 at kind of ok temperature.  I do think with both the element and themostat at the top, it probably isnt heating the full tank.