This is the process I went through to convert a cheap 30lt Tea Urn into a boiler for my new home brewery. The premise was to build up all the necessary kit for as little outlay as possible - "she" wouldn't let me do it otherwise... PICTURE_1 I got this from an online auction site for the princely sum of £10. It had been used only once and was in very good condition and if things didn't work out I had not lost much money. PICTURE_2 The plastic base is removed by unscrewing the three brass retaining screws and this reveals the electrical wiring built in to the base and a loose stainless steel ring that has the Mains Switch and two indicator lights - the only controls on this particular version of Chinese origin Urn. There are many similar versions of this type of urn for sale on the internet so the following wiring MAY be the same across the range but you may find slight differences in other types. PICTURE_3 and PICTURE_4 The various components of the urn are detailed in picture 3 with the circuit diagram shown in picture 4. This urn has two heating elements (G) that are connected to individual relays on the small circuit board (E) that are, in turn, switched on and off by the Max Temp Thermal Cutout (I) - the Keep Warm TCO. The Heating and Warming lights are switched at the same time as the relays showing the user what is happening. The mains supply comes in and goes directly to the double pole switch (B) and the printed circuit board [PCB] (E). Circuit Protection This is handled by two components. 1) The Thermal Fuse (C) hidden under a clamp in the middle of the heater base and shielded with heat proof sleeving is in the Neutral line and feeds the heating elements and the PCB. If this ever blows then everything will stop working and it MUST be replaced - under no circumstaces is this to be shorted out!!! 2) The Boil Dry Thermal Cut Out (H) is the first component in the mains Live feed and will switch everything off if the elements ever get too hot - it should automatically reset if water is added to the dry tank but I am not going to test this out. Circuit Action With the urn plugged into the mains, and the switch off, nothing will happen. Turning on the switch will supply mains to the printed circuit board as long as the two Thermal Cut Outs (TCOs) are closed. The red Heating light comes on as the two relays switch on and connect the heating elements to the mains. The water starts to heat until the Keep Warm TCO opens at 92 C. The relays then switch off and the heaters go off in turn. The Warming light comes on at this point - I won't explain why here but it does and things stay like this until the water cools down to the point that the Keep Warm TCO closes again. There is some hysteresis here so the water in the urn will be kept on or about the temperature of 92C. Modification To make this urn into a useful "boiler" we must change the temperature at which the relays are turned on and off. This is done by replacing the TCO (I) in the circuit with a variable control that can detect the heating temperature and switch the relays. I bought a BURCO HOT WATER BOILER TEA URN THERMOSTAT AND CONTROL KNOB (component numbers: 082620290 and 082620359) from the web (Picture 5) for ?26 to do the job. Removing the TCO from the base of the urn gave me a convenient place to clamp the temperature sensing bulb using a spare heat-sink clamp I had kicking about in my spares box (Picture 7). I drilled three holes in the base next to the Mains switch to mount the control (Picture 6). The wires that went to the TCO conveniently connect to the two spade terminals of the Burco control. The new circuit layout is now that shown in Picture 8. Note the detail in the picture showing the published APPROXIMATE temperature settings for the given value shown on the control knob. I have yet to test these values but I will make a note what the true values are when I do a further mod to the boiler to add a thermometer to the casing. Testing All that is required now is to check all the wiring - to see there are no loose connections or shorts - bolt it all back together, fit the control knob (Picture 9), put water in the boiler and power it all up. (Picture 10). Conclusion This modification worked very well and only cost me a total of ?36 to get a fully controllable boiler that can furnish me with hot water at a range of temperatures up to 103C (supposedly) for mashing and sparging - something I have yet to do but watch this space. After testing I was forced to do a further modification which will be detailed in a later thread.