Indirect Thermal Store pre heating to Combi?

[bernardgreen]

That was a cold water cistern connected to a open vented cylinder

The fault was the thermostat on an electric immersion heater failed to open and the water in the cylinder was boiling over into the tank in the loft

 

[Agile]

I was doing some work recently in a house where the unvented cylinder had popped and the side split open, emptying it's contents through the ceiling of the dining room. From what the customer was saying, the 2 port valve actuator broke and stuck open, and the pressure relief valve was jammed due to corrosion.

Cylinder had never been serviced in the 9 years it had been installed...

Apart from those two failures the THIRD protection device should have operated and that is the cylinder overheat stat.

Possibly never connected though. These cylinders are amazingly safe as long as they are properly installed which is often not the case.

Even if the T & P valve was jammed, there should still have been a 6 bar PRV at the inlet valve to give final protection against over pressure.

Interesting question though. Do some people connect the boiler on signal just through the two port as if it was an an "S" plan? Even so the boiler output temp should have been controlled to about 82 C and at that temperature I would not have expected the cylinder to have burst.

I like to control the boiler from the cyl stat, cyl o/h stat and the motor valve switch all in series.

Tony

 

[Dan Robinson]

That was a cold water cistern connected to a open vented cylinder

The fault was the thermostat on an electric immersion heater failed to open and the water in the cylinder was boiling over into the tank in the loft

And?

 

[Agile]

And the plastic tank was not rated for boiling water and deformed and collapsed spilling the water.

I think that the specifications for the plastic tanks have now been upgraded to ensure they can take boiling water for a short time.

There is also another similar fault where loft tanks are not supported on a water resistant base. Chipboard or MDF is NOT suitable.

Tony

 

[Dan Robinson]

the specifications for the plastic tanks have now been upgraded to ensure they can take boiling water for a short time

Would like to see that change documented? Perhaps @bernardgreen can rustle something up from Google How is holding boiling water for 20 minutes or so longer going to be of much use when you're asleep under the fecker when it goes? Does the new spec come with an alarm sounder?

another similar fault

Similar fault to boiling water pishing through the ceiling over your bed? How is a water resistant base going to help? Spread the torrent over a greater area perhaps? Great; 2nd degree burns eeevverywhere.


Sign me up.

 

[Steelmasons]

Don't forget that woman that died too. All of these deaths were from directly heated cylinders though. I was doing some work recently in a house where the unvented cylinder had popped and the side split open, emptying it's contents through the ceiling of the dining room. From what the customer was saying, the 2 port valve actuator broke and stuck open, and the pressure relief valve was jammed due to corrosion. Cylinder had never been serviced in the 9 years it had been installed...

What happened to the 3rd line of defence??
Which is the reason why all system controls should be switched via OH stat..

 

[Steelmasons]

Open safety vent pipe should discharge to drain , most commercial installations have adopted this practice..

 

[Echo the husky]

What happened to the 3rd line of defence??

No idea, I was there looking at some lights...

 

[Dan Robinson]

Open safety vent pipe should discharge to drain , most commercial installations have adopted this practice..

Did you do all your domestics thusly though?

 

[bernardgreen]

Would like to see that change documented? Perhaps @bernardgreen can rustle something up from Google

Do your own searching.

The incident happened because a thermostat failed. As a result immersion heaters are now required to have a thermal cut out as well as a thermostat. If the cut out operates it has to be manully reset, hopefully after the thermostat has been replaced.

 

[bernardgreen]

How is a water resistant base going to help?

Have a think.

Forget a scalding hot tank of water.

Think cold.... think about a cold tank in a humid atmosphere. Condensation runs down the outside of the tank and soaks into the MDF.

Sodden MDf cannot take the weight of the tank

 

[Dan Robinson]

Great.

Think I'll stick to my preference of a 25 year guaranteed laser welded vessel with its 7 point safety system.

Perhaps you can Google "loaded questions" when you get a moment.

 

[Steelmasons]

Open safety vent pipe should discharge to drain , most commercial installations have adopted this practice..

Did you do all your domestics thusly though?

Eh??

 

[bernardgreen]

with its 7 point safety system.

What are these 7 points ? safety devices such as pressure relief valves, if one fails will one or more of the other six ensure the cylinder cannot "go critical" ( as being in danger of bursting )

 

[DP]

with its 7 point safety system.

What are these 7 points ? safety devices such as pressure relief valves, if one fails will one or more of the other six ensure the cylinder cannot "go critical" ( as being in danger of bursting )

Function of a T&P valve is to discharge at 95 degrees C allowing cold water to enter cylinder thus cooling the body of water. That is just one of many safety devices fitted to unvented cylinders