The unvented cylinder annual inspection myth?

I can't find any evidence that unvented cylinders require an annual inspection.

T
Reply to
tom.harrigan
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Given their explosive potential in an overheat situation and a stuck pressure relief valve, don't you sleep a little easier if it's been inspected regularly? ;-)

It doesn't seem to be law but just prudent.

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Reply to
Tim Downie

If you buy a good quality cylinder (I'm going to get an Oso) and have the appropriate safety ancillaries installed I can't see the point in wasting time and money on an annual inspection by someone who has gone on a 0.5 day "course".

I became curious about this as it is supposedly one of the benefits of a thermal store that annual certificated inspection isn't mandatory. Yet another non-reason to get a thermal store!

T
Reply to
tom.harrigan

It's still a pressure vessel with explosive potential (more so than a vented cylinder). Safety ancillaries can and do fail. May not be hard to check yourself if you know what you're doing but I'm not sure I'd want to live on the other side of a party wall to one that hadn't been inspected for years. For most non-DIYers, annual inspection probably makes sense.

As long as it's not going to affect others you can decide what level of risk you're prepared to live with.

Tim

Reply to
Tim Downie

I think there is another misconception here as well. The only time a pressurised water cylinder is at explosion risk is going to be when it has the possibility of being heated to over the boiling point of the water content. Then there is the risk of the explosive production of steam should it rupture.

For a cylinder heated via a water flow from a boiler, the chances of super heating it seem minimal. (after all, pressure testing of steam or compressed air systems is often done with water because of its significantly lower risk - its lack of compressibility making it very difficult to store mechanical energy in it)

Reply to
John Rumm

Not true. It's a pressurised system with an air reservoir. If punctured, it will spray hot water at system pressure in a way that vented systems won't. That's itself a hazard (depending on location).

Any central heating system capable of sinking a trawler (look it up!) needs some degree of care in its maintenance.

Reply to
Andy Dingley

But if it has an immersion element, then that would change the risks.

Reply to
Rod

The point, that annual certificated inspection of unvented hot water tanks (at =A350+ a pop) is not mandatory. I had been mislead into thinking was is by people trying to sell me a thermal store. Being lied to irritates me!

It is non sequitur to assume no checking or maintenance will be done. I can assure you (never having had one of these things before) my checking will be daily for quite some time after installation, even knowing that there must be literally millions of the systems installed safely across Europe, and that mine (with its internal expansion chamber) is guaranteed for 25 years.

I will take your advice however, and refrain from attacking it with an axe!

T
Reply to
tom.harrigan

You're forgeting Sods law. The only time the safety valve is likely to get stressed is when your CH boiler packs up on Christmas Eve and you turn on the immersion element that's not been used in years. A sticky stat in that and a sticking safety valve can then lead to an explosive situation. A vented cylinder needs another level of system failure before it can blow.

The risk is low but it's a hgher risk than an vented cylinder.

Tim

Reply to
Tim Downie

So, just to summarise, for an unvented cylinder to be at risk of over pressure failure following oveheating:

a) The immerser must be in use and the stat fail and b) The manditory overheat stat must fail and c) The manditory over pressure relief valve must fail

Still scared?

Reply to
fred

I have an OSO unvented cylinder (it's in the garage with the oil boiler). I would like to check the safety valves myself, but where do I find out how?

R.

Reply to
TheOldFellow

Not terribly, no. Never was. But, all those things can fail silently and the first you might know of their failure is when your cylinder explodes. Of course it's rare and the Americans and continentals have been using unvented electrically heated cylinders for years and we don't hear of massive numbers of incidents.

It just cannont be denied that an open vented cylinder is intrisically less dangerous than a pressurised one. If I had one or lived next door to one I'd sleep easier knowing that somebody competant who understood the dangers had periodically checked the safety relief valve.

Tim

Reply to
Tim Downie

Agreed - hot water can come out in quantity and cause damage. It needs careful thought applied to its location in the same way that any stored hot water system does. After all, people have been killed by ordinary hot water cylinders when they have ruptured (or deposited their content into plastic cold water tanks) in lofts and deluged people asleep under them.

However, that is not remotely similar to the explosive effect you see on Dribble's oft posted link to a electrically heated sealed contained with all the safety features defeated.

I don't know to which incident in particular you refer, but I would presume if this was the result of an explosive blast from a water heater, then it involved superheated water / steam.

There was a case where an American high rise apartment block was brought down by a similar stored water system failure. (documented in the book "Why buildings fall down" IIRC:

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Reply to
John Rumm

Not really the same but this is what happened when the Mythbusters deliberately disabled all the safety features on an American-style water heater:

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Reply to
Reentrant

Yes it does - as would possibly a gravity circulated solid fuel stove.

Reply to
John Rumm

In article , Reentrant writes

upgrade it to 10kW to get it to do what their agenda wanted it to?

Reply to
fred

That's a good point that I'd fogotten about so that risk needs to be added to the vented tank side of the equation. After all, if you've no loft tank then that can't happen. I wonder how how many deaths have resulted from this? Not a lot I'll wager but then probably not too many people have been killed in the UK by unvented cylinders either.

Tim

Reply to
Tim Downie

I did like that episode made me smile not as good as the "clean out cement mixer with dynamite" for a big bang

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Reply to
Kevin

That'll need TWO sticking stats for the immersion heater and TWO sticking relief valves, one of which has two means of opening.

Reply to
Ed Sirett

Don't forget

d) The manadatory backup over pressure device /over temperature device.

Reply to
Ed Sirett

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