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Where else are separate hot and cold taps common?

Sorry, I meant "no vented outside the UK".

Sorry I meant "no vented outside the UK".

Maybe, I have never inspected any plumbing there, although I would guess there might be some vented there. They don't seem to exist in Germany and Switzerland. One should be able to tell by the existence of separate hot and cold taps, since vented hot is not technically potable. Separate hot...

That is just silly, there are no vented systems outside the UK, so I guess no explosions. You cannot say vented are safer outside the UK, because they don't exist. Inside the UK there has never been an explosion of an unvented cylinder, despite millions installed over the last 34 years since...

I don't see a hundreds of stories about unvented cylinders exploding. Statistically, in the UK unvented cylinders are no more likely to explode then vented.

Funny how when I lived in Canada, the land of direct-fired gas cylinders, I never heard any "stories" about water heaters exploding. Are you sure they are not just mostly "stories"? If you dig a bit, you will find most stories of cylinder explosions are caused by gas leaks.

I think the only hot water cylinder explosion so far in the UK was on a boat, and it was a vented cylinder. Gas explosions occur far more often. Unvented is just not much of a risk.

In the UK I suppose, as they are mostly the only ones still using unvented systems. In the rest of the world, it has long been proven that unvented cylinders are not an explosion hazard.

But in practice, this does not seem to happen. Even in Canada where all they have is a single PRV, and there is a gas flame directly under the cylinder. And what makes a vented systems any safer? What happens if the entire mess in the loft freezes solid? IMO a vented cylinder should also be...

There can be, and almost always is, a great deal of debris in a typical North American water heater. They run until they rust out, but they don't seem to explode. In a CH system with a sealed boiler there is also a PRV on the boiler, so I guess both would need to be somehow blocked. I...

Deliberately plugging the PRV and removing the thermostat is not a very realistic scenario. And I suppose you could also do that with a vented cylinder, just plug the vent pipe and do the same.

I was arguing about simplicity rather than safety. Here is what a standard water heater looked like in Canada when I lived there, and I have not heard of one exploding do to PRV failure. Notice the PRV just dumps on the basement floor, there is no expansion tank or check valve, and the device...

I think this is what in the UK is called a thermal store. Is a feed and expansion tank with all its associated piping (including overflow), really simpler than a PTRV, drain, and an expansion vessel?

No, I meant boiler - vent - feed - pump.

Mine is the latter, but the F&E pipe is upstairs in an airing cupboard, just below the F&E tank.

It is all about oxygen intrusion.

I am not so sure. Some vented systems are clean, whereas others (like mine) are horribly corroded. If your sealed system loses pressure, you need to find and fix the leak. Just replacing the water is not really a solution.

The advantage would be to limit corrosion. For a heating system, I can't really see any downside to sealing it, replacing the F&E tank with an expansion vessel, and running it at 1-1.5 bar, with a 2 bar relief valve.

It makes sense to avoid pipework that allows the pump to push/pull water up into the F&E tank. There is also the expansion of the water itself to consider. If one checks the level in the tank cold, and then looks again once the system has heated up and the pump is off, there will also be a...