Any gotcha's to drain and refill a hotwater tank to replace 2 x immersion heaters?

[Chester]

Unvented immersion Sod easy to undo compared to the older ones usually cos rely on rubber seal. Make sure you buy the correct type of immersions, the standard ones from screwfix are not the same thread size.

Providing you're qualified

 

[Ric2013]

Technically no as it doesn’t interfere with any safety components

Is that the case? Given that the thermostat in the thermostat could be argued to be a safety component. If you're right it means I once turned down a job unnecessarily...

 

[GerryB]

It's the replies regarding G3 cert that have really helped here. They prompted me to read and become more aware of the safety aspects of unvented cylinders, so I will focus on getting more quotes, include a service as I suspect one has not been done for at least 4 years and specifying titanium immersions.
Thanks all.