Does this water heater need a 'safety valve'?

From the installation manual at:

Where this is not possible the installer will need to fit a set of cold water controls.

Note: If a valve i.e. a non return valve, water meter, pressure reducing valve or any type of valve or fitting that acts as a non return valve is installed on the cold water mains, this will prevent expansion. Therefore it will be necessary to install an expansion vessel (see pages

Note: If in doubt always install a pressure reducing valve (limited to

Anything for the UK market, and has a water volume of under 15 litres, should be self contained, and have all relevant safety devices fitted internally. Above 15 litres is subject to the G3 Building Regualtions notification, and should only be fitted by a competent person who has passed the G3 course.

None of which addresses my question, is a pressure relief valve needed?

This is not an expansion vessel or a pressure reduction valve.

Ah, thank you, this is under 15 litres so should be 'self contained'.

Unlike this larger one which sunk the boat.

GH

It does address your question by saying that expansion can either be absorbed by pipework under certain conditions or using an expansion vessel.

I can assure you I never said your unvented heater was an expansion vessel and don't understand the basis of your post. You might consider getting a professional in if you believe the installation instructions don't recommend the use of an expansion vessel or a pressure reduction valve.

If a pressure relief valve was recommended we can be certain the manufacturers would have specified one in their instructions.

But that's the whole problem, they don't. As I quoted before all they say is:-

Some countries may require the use of hydraulic special safety devices: the installer must check the suitability of the safety device he tends to us.

I am happy that I have enough expansion available in the incoming cold pipework but there isn't a definitive yes/no requirement for the pressure relief.

Coo! :-), or maybe :-(, at least all those on board were rescued OK. It's not that much bigger than our boat, 17m as opposed to 11m, however the hot water system was 120 litres as opposed to our puny 10 litre one. No wonder there was a big bang!

Still, I think I want to be on the safe side with ours. The old (also

What is feeding it with cold water? Is this the boat's water pump? If so that presumably has no possibility of backwards flow to accept expansion. Boats sometimes have an accumulator on the output of the water pump to prevent rapid cycling and random pulsing when not being used due to slight leakage. That would presumably accept considerable expansion?

nib

It's all flexible (i.e. braided PVC) pipe between the pump and the water heater, several metres of it, so there's loads of expansion capacity. There's enough expansion for the pump not to cycle on and off during use and it only mutters to itself once every several hours.

I don't understand your argument why you would even need a pressure relief valve?

If you're desperate to fit one then do.