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

 

[Knobhead]

The water tank can’t get any hotter than the temperature set on the boiler. So it’s a bit basic but nothing wrong with it.

 

[egginyourface]

I haven't seen the cylinder but think its a megaflo. Doesn't the valve act as safety device, ie shut down the boiler etc

 

[RmBo_0]

Sounds like its been changed from s plan to c plan for some reason. But don't think it's dangerous myself.

 

[egginyourface]

Thank u both for replies

So what's the point of having a valve for hot water if its not needed?

 

[Knobhead]

The H/W valve diverts all the boiler output to the heating. No other reason.

 

[Deleted member 9648]

I haven't seen the cylinder but think its a megaflo. Doesn't the valve act as safety device, ie shut down the boiler etc

....all it does is switch off the HW when the tanks are up to temp.....sounds to me like it has failed,been locked open to get the system working,and never got changed.

 

[egginyourface]

Sorry If this sounds daft, but whats the point in having 2 port valve for hot water if its not needed?

 

[londonlec]

You need a G3 qualified plumber to work on these, as you say, I am 90% sure this unvented cylinder needs a 2 port zone valve as part of its safety mechanism.

 

[snowhead]

In the past it was common to have no valves.
The Hot water temp relied on the boiler setting and the heating was controlled by pump on or off.

However if it's an unvented, which Megaflows are, it MUST have a normally closed 2 port valve on the boiler flow to the cylinder controlled by a safety over-temp stat on the cylinder.

It needs someone with G.3 to sort it out.
Plumbers aren't the only one's with G.3

 

[egginyourface]

Your right. It's a in unvented cylinder. Had a look at it today. I'm not involved with the system myself but out of curiosity opened the junction box and noticed the hot water 2 port valve has been disconnected. Theres a 3 core whicj leaves the jb and goes upto cylinder in the loft. I asked the plumber why he hasn't re instated it and he said it works fine with out it.

Now I'm interested in learning how these systems work and have feeling this is unsafe.

 

[londonlec]

I personally (as a spark!) think it is unsafe and contravenes G3.

The 2 port valve is often supplied by the manufacturer of the cylinder, they wouldn't hand you a £50 zone valve for nowt ;-)

 

[SYKRAPS]

If it is a megaflow unvented cylinder you DO need a 2 port valve for the DHW connected as a safety cutout to stop the cylinder overheating, I have been lead to believe that these systems can be like a ticking time bomb waiting to go off without it.

http://www.plumbcenter.co.uk/wcssto...l/ti/on/HeatraeSadia_Megaflo_Installation.pdf

 

[egginyourface]

Sorted it with client. Have arranged for engineer to go round tomorrow

 

[Spark1979]

Its definitely needed how can you shut heat off to cylinder if central heating is turned on the water in the tank will boil without the valve to shut it off

 

[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