Immersion boiler not heating water hot enough.

Chrysalis

nofoollikeold said:

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.  

Thanks for this info, I will mention it when I next see the plumber.  If that isnt soon I will request him to come down to speak to him about it.

Chrysalis

Thankfully will be going back to gas for water, so I will leave this be.

EssexHebridean

Really glad to hear that. Could I suggest that if you are not intending to use the immersion again, that you re-set the thermostat back to 60° max?  This covers a future situation where you move out and the new people decide to use it - for whatever reason - without knowing about the far higher than standard temperature. If you did need to use it yourself again you now know how to deal with it of course. 

Albermarle

Chrysalis said:

Thankfully will be going back to gas for water, so I will leave this be.

As said in a previous post, if you have the boiler flow temperature high, to make sure the hot water is very hot ( as you like it) then it will also mean the hot water flowing to the radiators will be on the hot side. ( Unless unusually you have two separate settings for hot water and heating).
The problem with having the boiler flow temperature high is that the boiler runs inefficiently, and you will be using more gas. 

FreeBear

Albermarle said:

Chrysalis said:

Thankfully will be going back to gas for water, so I will leave this be.

As said in a previous post, if you have the boiler flow temperature high, to make sure the hot water is very hot ( as you like it) then it will also mean the hot water flowing to the radiators will be on the hot side. ( Unless unusually you have two separate settings for hot water and heating).
The problem with having the boiler flow temperature high is that the boiler runs inefficiently, and you will be using more gas. 

An intelligent timer/thermostat with a modern boiler should be able to do Priority DHW  and call for a higher flow temperature when required. Running constant at a flow temperature of 75-80°C will mean a fuel efficiency of 86% or worse. Dropping the flow temp down to 70°C or lower for heating should get 92% or better efficiency. On top of that, there will be less wear & tear on the boiler, so hopefully fewer breakdowns.

With a DHW temperature of 70°C, there is a very real risk of nasty scalds. Even at 45°C vulnerable people are at risk of scalding. If you must keep the DHW cylinder at such a high temperature, it would be prudent to fit thermostatic valves on all the taps.

Albermarle

An intelligent timer/thermostat with a modern boiler should be able to do Priority DHW  and call for a higher flow temperature when required

I think when this came up in another thread, there was some comment that even many modern boilers do not have this facility? Just specific ones ?

Chrysalis

EssexHebridean said:

Really glad to hear that. Could I suggest that if you are not intending to use the immersion again, that you re-set the thermostat back to 60° max?  This covers a future situation where you move out and the new people decide to use it - for whatever reason - without knowing about the far higher than standard temperature. If you did need to use it yourself again you now know how to deal with it of course. 

Probably will be doing that anyway once I am using the new boiler for water, as I like to leave things as they were.

FreeBear

Albermarle said:

An intelligent timer/thermostat with a modern boiler should be able to do Priority DHW  and call for a higher flow temperature when required

I think when this came up in another thread, there was some comment that even many modern boilers do not have this facility? Just specific ones ?

If a boiler can alter the flow temperature on command by the thermostat, then it will be able to do PDHW. Any OpenTherm, EMS, MBUS, etc compatible boiler that can modulate will have that ability.

Martyn_H

I had the same problem with getting hot water but not much of it, and the cause was a burnt out element. A replacement was approx £30.

Chrysalis

Martyn_H said:

I had the same problem with getting hot water but not much of it, and the cause was a burnt out element. A replacement was approx £30.

Well in my case the element was swapped, as it was done with the thermostat.

The same tank is used with gas, and when its heated  by gas it doesnt have the same problem (the immersion thermostat isnt used in this case), so I am fairly confident issue is because there is just a single thermostat at the top for the immersion, which means colder water at the bottom doesnt get fully heated.

I will change its setting back to 60C probably tomorrow, as I am using gas again for water now.