PTFE tape/SIlicone grease around threads??

i use both, better safe than sorry,

 

for rad tails use ptfe tape, for the immersion you would need a couple of rolls to make any impression on the thread !! normally supplied with fibre washer, use silicone will take up any differences in male and female threads

 

Ptfe tape is used to seal the threads on the rad tails and pipe connections to the DHWC. In the case of the DHWC connections you will need a fair bit. Normally 8-10 turns of ptfe is enough for a rad tail. For DHWC connections up to 15 is necessary. Also I use the PFTE tape as string to form a wedge at the base of the thread, this compresses as the connector is screwed in and acts as a final seal.

Silicon grease can act as a sealant but I mainly use it to lubricate. In the case of the immersion heater, the main seal is the fibre washer. The two mating surfaces either side of the washer should be clean and flat. Some grease added to the threads reduces the friction and allows the heater to be tightened up using less turning force and so give a better seal at the washer.

Adding ptfe tape to the immersion heater should not be necessary but could be added to help. Not too much though since it can cause the heater to be too stiff and put too much force on the cylinder.

I use ptfe tape and silicon grease as my main methods of sealing since they are both totally benign to any other fittings such as shower mixers.