Open vented hot water. Explosion situations?

[chesneyharris]

With open vented hot water systems, what situations (s) can occur such as a fault(s) that could cause an explosion?.... I have heard there is a chance of it, but am not sure how? And would like to for obvious reasons? I know the cylinder has a vent pipe to take away steam if the boiler thermostat does fail?.... Anyone able to help me please?...

 

[electronicsuk]

I'm not sure about vented system explosions - I think the majority of incidents involve boiling water rising up the feed/vent pipes resulting in splitting of the plastic header tank. Anyone unlucky enough to be underneath it is, obviously, going to suffer quite serious injury.

 

[chesneyharris]

Is read about this in a newspaper over a year ago. That is why new immersion heaters have an overheat stat and most modern boilers also have an overheat stat/thermistor. Maybe if the vent pipe become blocked/frozen up etc and the stat failed there would be an explosion....

 

[charliechaplinspants]

An unvented cylinder has no tank/pipe for expansion of the hot water, expansion vessels are normally fitted externally but some already come with them internally. They also have a blow off mechanism like a combi should the expansion vessel fail or the cylinder become over pressurised for whatever reason, if installed incorrectly by incompetent persons they have been known to over pressurise and explode.

 

[nickso]

An unvented cylinder has no tank/pipe for expansion of the hot water, expansion vessels are normally fitted externally but some already come with them internally. They also have a blow off mechanism like a combi should the expansion vessel fail or the cylinder become over pressurised for whatever reason, if installed incorrectly by incompetent persons they have been known to over pressurise and explode.

have i just fallen for a wind up or do you really not know what you are on about?

 

[chesneyharris]

i know that with unvented systems you have to be specially trained to work on them. and that they have also a temperature relief device that opens if both the stat and overheat cut out fail. Thyy also require a 2 port motorised valve as a normal 3 port is always open to the hot water, so would not spring return shut if the stats were satisfied.

Yes the expansion valve /prv opens if the water pressure is above for eg 3 bar or if the expansion space/charge has gone.

Still not sure about the open vented ones though... ???

 

[mickyg]

vented cylinders are not known to explode as they are vented, so no build up of pressure can occur. I think what you are thinking about is when the immersion fails and boiling hot water fills the storage tank, melting/cracking it and releasing scoulding hot water onto any unsuspecting individuals below. This happened some time ago and caused a fatality, hence the new regulations.

Additionally, please note as I've pointed out before that Charliepants is "special" so please take any comments with a pinch of salt.

 

[chesneyharris]

thank you for your info. i suppose that if the boiler stat were to fail, i'd get pumping over. and this could be very dangerous as tmy feed and expansion tank is plastic.

 

[glasgowgas]

thank you for your info. i suppose that if the boiler stat were to fail, i'd get pumping over. and this could be very dangerous as tmy feed and expansion tank is plastic.

this has happened, widely reported in the media, resulting in the death
of a wee baby. an absolute tragedy, and the best reason for, at any opportunity for removing them and changing system.

 

[charliechaplinspants]

thank you for your info. i suppose that if the boiler stat were to fail, i'd get pumping over. and this could be very dangerous as tmy feed and expansion tank is plastic.

I do apologise, I mis-read and was on about unvented heating systems, probably need my glasses, nice to know that some of the other guys on the forum are on hand to correct me almost instantaneously though.

 

[steved101]

Make sure your feed & expansion cistern is fully supported correctly across its whole base and more.

 

[glasgowgas]

Make sure your feed & expansion cistern is fully supported correctly across its whole base and more.

won`t stop a plastic one melting.

 

[steved101]

true but may support it a bit better if a fault occurs and give the occupier more time to deal with the problem and get it sorted.

 

[glasgowgas]

true but may support it a bit better if a fault occurs and give the occupier more time to deal with the problem and get it sorted.

that is also true sir.

 

[steved101]

OP - yes a blocked vent pipe would cause an explosion if the stat failed.

Also a blocked vent pipe and cold feed pipe (ie due to freezing in the loft and being uninsulated) - can lead to CYLINDER IMPLOSION (when a tap isopened the pressure in the cylinder falls to BELOW ATSMOHPERIC PRESSURE and can cause the cylinder to deform.