TESLA TIH650 27 Inch 27" Replacement Incoloy Immersion Heater With 18 INCH 18" Incoloy Thermostat 3Kw 2 1/4 Boss Anti-Corrosive

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Product Description:

TESLA TIH650 27 Inch 27" Replacement Incoloy Immersion Heater With 18 INCH 18" Incoloy Thermostat 3Kw 2 1/4 Boss Anti-Corrosive


  • ELEMENT LENGTH:  27" (other lengths available - see table below)
  • POWER: 240 volt, 3 kW
  • ELEMENT BOSS: 2.1/4″
  • THERMOSTAT:  Incoloy - High Limit & Control
  • WATER TYPE:  Suitable for Medium to Hard Water Areas
  • SYSTEM TYPE:  Vented
  • CYLINDER SUITABILITY:  Suitable to be used in Stainless Steel and Copper Cylinders.   
  • RoHS compliant
  • BEAB Approved- Registration number E9573BS EN ISO 9001
  • Guaranteed 12 months, providing correctly installed and only subject to Normal operating conditions
  • Anti - Corrosion
  • PURCHASE RIGHT FIRST TIME:  We would rather help you identify the correct immersion rather than you having to return a product as wrong item bought and delaying your fix.   Contact us at customerservice@fixthebog.uk if you have any queries or read below which may help you with any queries.


There are 5 possible reasons for the immersion heater to stop working

  1. There is no electricity supply to the immersion heater.
  2. The over temperature trip in your Immersion heater’s thermostat has cut out.
  3. The thermostat in your immersion heater is faulty.
  4. The immersion heater has failed to earth.
  5. The immersion heater has gone open circuit.

Assuming you have identified a new immersion is required and your old immersion is not a Tesla and you need help determining the correct immersion to purchase, there are a number of factors that need to be considered.  Whether it be a vented, unvented, economy 7, solar system, copper or stainless steel cylinder and side or top mounted.

  • Selection of the boss/head size, kW requirement, length of the immersion heater, and finally the correct immersion heater material that is conducive to the water hardness in your geographical area (see link above under Product Details)

    • What Water Hardness is your area - Click here to see your area for Water Hardness :
      • Soft water areas - Fit copper.
      • Moderate to hard - We recommend fitting either incoloy or titanium.
      • Hard to very hard - Incoloy will suffice but we highly recommend fitting titanium which will last longer.
    • Most Immersion heaters have a product code either on the side wall of the cover or on the top of the cover. This code will be a series of letters and numbers please see images. Send a photo of this to us and we will confirm a like for like replacement.
    • If your immersion has no codes please provide to us:  
      • the length of your immersion heater
        • Measure from the underside of the brass boss to the end of the heating element. However if your immersion heater is fitted in the side wall of your hot water cylinder (horizontally) then it will usually have a length of between 11 and 16 inches. If it is fitted to the top of your hot water cylinder (vertically) then it usually has a length of 18 to 36 inches dependant on the size of your hot water cylinder.
      • the Power rating in watts
      • the size of the thread of the brass boss
        • All domestic immersion heaters have a BSP thread size on the brass boss. The actual measurement across the diameter of this boss is 0.25 inches larger than the stated BSP thread size. For example a 2.25 inch BSP thread will have a diameter of approx 2.5 inches see attached illustration.
      • whether your hot water system is vented or unvented
        • Unvented cylinders work directly from the mains supply of water and are essentially a hot water storage cylinder
        • Vented cylinders are connected, via a vent pipe, to the cold water storage tank which is usually located within the loft space of most properties.

Part P disclaimer regarding fitting of Immersion Heaters and thermostats.  It is a legal requirement that these units are fitted by a competent and suitably qualified person in accordance with Part P of the Building regulations and that installations are compliant with all local national rules and the IEE wiring regulations.


Before fitting the immersion ensure you understand all of the potential issues that would invalidate the warranty.   See the Tesla advice here


Material: Element/Thermostat

  • Copper / Copper:   Not suitable for stainless steel cylinders.   For soft water areas only  
  • Incoloy / Copper:     Not suitable for stainless steel cylinders.  Suitable for medium to hard water areas
  • Incoloy / Incoloy (this listing):    Suitable for stainless steel and copper cylinders.  Suitable for medium to hard water areas
  • Titanium / Titanium:     Suitable for stainless steel and copper cylinders.  Suitable for hard to aggressive water areas
  • Dual Heaters (copper):     Includes dual safety thermostat and 1m cable
  • Rod Thermostats
  • Unented 1 3/4"
  • External Heater:     Also known as Willis/Geyser
  • Plug-in Thermostats:     Suitable for use with upper or lower immersion heaters on Unvented Cylinders


  • Plugs
  • Washers
  • Flanges
  • Cylinder Flanges
  • Spanners

THIS LISTING IS FOR THE The Tesla Incoloy with Incoloy Thermostat Pocket range.  To view other sizes in the range click links in table below:

TIH640 11" Element with 7" Thermostat FTB778 here
TIH641 11" Element (1 kW) with 7" Thermostat    
TIH644 14" Element (2 kW) with 11" Thermostat 1 3/4" Head (for Unvented Cylinder ONLY)    
TIH645 14" Element with 11" Thermostat FTB779 here
TIH646 14" (30") Dual Bend Element with 11" Thermostat FTB780 here
TIH647 18" Element with 11" Thermostat FTB781 here 
TIH648 23" Element with 18" Thermostat FTB782 here 
TIH650 27" Element with 18" Thermostat FTB828 This listing!
TIH651 27" Element (2 kW) with 18" Thermostat    
TIH655 30" Element with 18" Thermostat FTB829 here 
TIH660 36" Element with 18" Thermostat FTB830 here 








Q1. Should I use a sealing compound on the thread?
A1. No, you only really need to use the washer provided although PTFE tape may help if needed. Also, 
make sure all sealing surfaces are clean before fitting the element and that no sealant gets into the tank or on the element itself.

Q2. What is the red brace for on some longer elements?
A2. This should be removed before fitting as it is for transit support only.

Q3. Why is the new side mounted element I fitted making a boiling / bubbling noise?
A3. Possibly because the element is not the same model as the one that was removed. Recommend to turn the temperature down

Q4. Why is the water just getting warm and not hot?
A4. Try increasing the temperature that the thermostat is set to, but please ensure that the correct size 
of element has been fitted to the cylinder.

Q5. There is a covering of something on the sheathing of the immersion heater and it has stopped working. Why?
A5. This will probably be a covering of limescale which has come from hard water and has effectively ‘choked’ the element. A new element of either Incoloy or Titanium should be refitted.

Q6. What can I do if the circuit breaker trips at the board when the immersion heater is turned on?
A6. Generally, this will be because the circuit breaker is of insufficient rating. Please ensure that the 
circuit breaker fitted has a minimum rating of 25amp and is on its own circuit and that nothing else is connected OR the element has a ‘dead short’. Please consult a qualified electrician if in any doubt.

Q7. Why don’t you put a temperature indicator on the thermostat anymore?
A7. Only because people expected an exact temperature to be maintained. The original markings were 
for guidance only to show the temperature limits. Now, we only use a ‘+ or –‘, albeit the lower setting is generally around 40 Degrees C and the upper setting is around 68 Degrees C. Do not over turn the dial as that will cause irreparable damage.

Q8. Why is the wiring inside the head of the immersion heater burnt?
A8. Invariably this is due to an electrical short. Ensure that the wires into the thermostat are securely 
in place and the retaining screws are suitably secured onto the bared copper wires but NOT over tightened.

Q9. Why is there water in the base of the brass head of the Immersion Heater?
A9. That means that there is a potential leak through the thermostat pocket. Please contact us.

Q10. Why with the old immersion heater could we get steaming hot water and now the new one is nowhere near as hot?
A10. The new EN standard means that we cannot allow the upper limit of the control thermostat circuit to rise above 70 Degrees C as this will cause ambient temperature problems with nuisance trip outs due to interference with the secondary safety circuit.

Q11. I have fitted one of your titanium immersion heaters but it doesn’t work. I’ve checked the wiring and made sure the electric feed coming in is switched on. The tank is full of water. What else could be wrong?
A11. There could be an electric fault, eg a faulty neutral wire could have melted the unit.

Q12: I fitted one of the immersions which worked for a number of months but then stopped. At first I was able to reset it but when it happened for a third time it would not reset.
A12: On return of the unit and inspection by manufacturer it was assessed and identified that the screw was not fully screwed down and therefore the unit had ‘arced’ and got really warm, ie an installation error.

Q13: I recently ordered a titanium immersion heater but it is not working.  I've checked my wiring and made sure electric feed coming in is switched on. Tank is full of water. Am I missing something?
A13: Customer later replied ‘I got an electrician to check the issue. Turns out it was a faulty neutral wire which melted the unit so nothing to do with the immersion heater.

Q14:  I've had problems remove an old immersion previously.  Any tips?
A14:  Start spraying the thread with WD40 or similar a few days before you try to remove it.

Q15:  Any tips before starting to replace?
Make sure that the isolation valve (if there is one) supplying the cylinder is functioning ok before you start. 
         Tie up the ball valve of the expansion tank in the loft as a precaution - better than turning off the cold water supply to the whole house (could be while before it can be turned back on again!).
         If your plumbing is quite old, and things like stop taps and isolation valves haven't been disturbed for a while, it might be worth having a pipe freezer kit on stand-by.
         Make sure that you have plenty WD40 or similar
         If the old element is quite stubborn to shift, and you need to give it a few bangs with a hammer, make sure that the cylinder is full of water to lessen the chances of damaging it.
         Have plenty of towels ready...

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