Let's see I'll have to do the figures for that. For a nominal 2.7a through 5 ohms thats 35.45 watts. That pretty well means ceramic wire wound resistors, and a heat sink. Also for reasons of convenience price and size I'd want to get three 15 ohm 25 watt resisters to connect in parallel. (only 12.5 watts is dissipated by each resistor a 2.7a, the excess capacity for heat dissipation can be a safety factor for higher nominal voltages, )
The only problem I could see with this is the heat that would be generated, how to mount them and put a vented steel cage around them for safety, A mistake here might be more dangerous than the original heating element could ever be.
There are after market 120v 325w elements available in the USA, I believe costing about $45 which might be cheaper and easier than using resistors.
Actually I thought about the resistor but for the above reasons went with replacing the element. The element itself just sits in a tube like holder against the boiler, there's only two wires, it would be very hard to go wrong.
BTW I took pictures as I did mine in freezing weather, so it didn't take all that long.
Cheers Willis
