Heating system with only one two port valve. Is this dangerous ...

[egginyourface]

Came across a heating system which had only 1x 2 port valve which was used only for the heating. There was another valve which had been disconnected from the mains but set in open position. I assume this was for the hot water.

Then From the junction box there's one three core going up to 2 x cylinders in the loft. Am i correct in thinking this is dangerous?

Shouldnt there be a valve to control hot water to cylinders

 

[egginyourface]

I Can't believe it's been left like this all this time

 

[Spark1979]

Bet their water was nice and hot though

 

[TAZ]

Yes this this valve is very important, it is the first line of defence in order to stop the stored water from going above 100c in the first place, the cylinder stat controls this valve (60/65c if that fails the overheat stat will operate at around 85/90c if it tries to go above that, the temperature & pressure relief valve will begin to open to let in more cold water to keep the temperature below 100c there is also a cold water expansion valve usually on the combivalve that comes with the unvented cylinder to provide additional safety This 2 port valve is still required even if there is a mid position valve in place.

 

[egginyourface]

Yes i remember seeing it on a yplan heating system. I was confused when I saw a three port valve followed by a 2port valve until some one explained it was for safety.

Do all unvented cylinders require the additional cylinder cut out stat?

Ive seen what cylinder does when it blows, not a pretymsite

 

[james29022004]

It will still get no hotter than the output of the boiler valve or no valve

 

[egginyourface]

What do you mean James?

 

[egginyourface]

S what causes them to blow up?

 

[james29022004]

it is an indirect tank which relies on water from boiler to warm up water in tank.All modern boilers i know of wont circulate or heat water above 82 deg

 

[egginyourface]

But what causes cylinders to actually explode?

 

[james29022004]

I would imagine the most common cause would be linked to a faulty immersion rather than overheating from the boiler itself(imersion is a backup to the indirect heating)
Or incorrect installation with shut off valves between tank and pressure releif valvee

 

[james29022004]

Unvented Water Heater
This link explains why a tank may rupture quite well

 

[TAZ]

AS others have said there is a whole raft of safety devices that would have to be breached before one of these ruptured. as the water inside the vessel is above atmospheric pressure, as the pressure rises so does the temperature. At 3 bar the boiling point in the vessel can be 144c if at this temperature the vessel was to rupture the water in side drops to atmospheric pressure causing a steam flashover which is capable of destroying the dwelling in which it is housed.

 

[egginyourface]

Ok. It's been confirmed that there are 2 x 2 port valves next to each cylineder.

looks like the,installer has wired up a junction box to provide neutral and permanent live to valves in the loft and dropped a 3 core from the loft to the junction box on the ground floor. Which works with boiler.

Seems a bit of a mess to me

 

[egginyourface]

And bit dangerous as the system will need to be isolated from 2 different locations to be worked on safely

 

[james29022004]

what circuit have they used in the loft?
Plumbers are not averse to using cpc as switched live either