Electric Immersion Tank + Thermostat

[daz240]

Hi

Over the past few days my hot water tank hasnt been heating up the way it should and in the morning we have no hot water.

Im in a flat with no gas so i have an electric immersion tank with two heaters (Overnight and boost)

i know that the thermostats are normally the problem and after listening to the tank at night when it ticks over it sounds like there is hissing coming from the heater but not as much as there normally is and not as much the the boost heater.

So today i was going to swap round the thermostats and see how it went tonight. On taking the covers off on both of the heater it seems like the wire positions on the thermostat are different. They are both the same thermo (Backer BT7) there are two wire locations one for the brown wire and another for a white wire that attaches to the heater. On the two i have they are both wired differently, they have both worked for the last two years.

So my question is doesnt matter where each of the two wires are connected to the thermostat???
Cant find anywhere online that will tell me?

 

[somersetsparks]

No not at all. Is uppose I am supposed to say that you should 'call an electrician' but I think anyone hsould be capable of doing this just make sure you switch it off.

 

[Clive P]

Hi,

Are you saying one of the elements is still operational and the other has failed, or both? Before I changed the stats over I would be first checking the element to see if that is at fault. Is the MCB still in or has it tripped? Do you have the means to check the element?

Regards.

 

[KAS1]

think of it as a switch on/off it's not like a non return valve or a diode

 

[daz240]

My over night heater is the one that doesnt seem to be working correctly.

it seems like the heater has life as i can hear very faint hissing when my electricty flicks over to the cheap rate over night.

The job seems simple enough i took a picture of both of the thermostates then proceeded to take them both out. When i tried to fit the lower one into the bottom i saw that on each picture the wiring was different. So i put it all back and thought i would do some research.

One thing i did see that was very odd - As i said the thermostates were both exactly the same (backer BT7- with same labels) appart from the point that slides into the tank(heater). One was like a spear or a golf tee and the other seemed to have been flattered at the end on two sides making it an X shape. This X shapes seemed to hinder the thermostate from sliding into the lower over night space.

 

[daz240]

Yep also to confirm all power has been turned off at the fuse box and is safe.

Changing the thermostate looks simple enough - anything more then i wouldnt attempt it.

 

[somersetsparks]

just different age of stats bate the bottom one has probably been replaced before as it gets used more. It sounds more like your element could be going TBH but your doing the right thing checking the stats first. Do you have a multimeter

 

[daz240]

no means to check the element - but it seems to hiss when the power flicks over to cheap rate. But it doesnt hiss as much as the working one above when that is turned on.

i had the element changed maybe a year or 2 ago.

 

[daz240]

i have a multi meter but im not that clued up on where i should be testing

 

[somersetsparks]

Just test on resistance with your meter (200 ohm setting) between the neutral terminal (Where the blue wire is connected) and the white wire with the POWER OFF. You should get a reading of about 16-18 ohms

 

[Guitarist]

Be careful here. Some stats have the safety cutout built-in and some require a separate unit. I realise that it seems a simple job, but you really should get a local qualified electrician in to sort this for you. If you live in a hard water area then it could even be an element scaled up and operating poorly. The only way to know for sure is with proper diagnostics. A good electrician will also test your earth loop impedance at the element to ensure the system is all connected properly, along with the RCD protection if you have any.

 

[lauriehurman]

I agree with the others. Usually - water boiling, thermostat - water cold, heater element.

As Somerset says, safe isolate, disconnect the wires from the element, test the resistance of the element with your multimeter. Don't test with the wires in place.

Remember - you are on an ELECTRICIAN's forum, we have a right to expect that your understand how to safe isolate etc.

Laurie

 

[daz240]

Hi, I have been away a lot recently so I have not had a chance to do anything with the water heater. But just before I went away my new thermostat got delivered. It is slighty different to the one I have in place already but probably only because the temperatures are not printed on the top. So my question again is really... does it matter on this one where I put the wires into it. I have notice on the top that there are plus and minus signs but im guess that is just for temperature and not +/- to do with the wire placement. Sorry to be a pain but I just just want to cause myself more problems. Let me know what you think. Thanks

 

[daz240]

Here is the picture of the new thermostat

 

[Guitarist]

Did you say that there was a separate safety cutout device?
If not, the stat you are showing is not suitable..

 

[daz240]

Here is a picture of the old one in place

If this doesnt work i will have to call someone out (All my fuse box will be turned OFF while im doing it)

Just need an answer about wires on this one


- - - Updated - - -

Just put a piture of the old stat in place on the tank - dont know if there is a cut out ....!?

 

[daz240]

Did you say that there was a separate safety cutout device?
If not, the stat you are showing is not suitable..

Just put a piture of the old stat in place on the tank - dont know if there is a cut out ....!?

​

 

[somersetsparks]

No there isn't. You should buy a new stat with built in cut-out like this Dual Safety Thermostat 7" | NoLinkingToThis.

 

[daz240]

No there isn't. You should buy a new stat with built in cut-out like this Dual Safety Thermostat 7" | NoLinkingToThis.

Wont that need to be wired up differently to the one i already have?

 

[Guitarist]

No there isn't. You should buy a new stat with built in cut-out like this Dual Safety Thermostat 7" | NoLinkingToThis.

Agree. Do not fit the stat you showed earlier. It is not compliant unless fitted with a separate safety cutout device.