Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwasher

[russ01]

While fitting a new integrated dishwasher I had to turn off the mains supply to replace a faulty isolation valve. All went well. Water back on and carried on altering doors and plinth etc. Around half an hour later water started to drip through the ceiling at the top of the stairs.

I got up into the loft to find water pouring from the 12 month old Gledhill Stainless lite solar cylinder. It had a big crease across the front of it and looked like it had imploded. I turned the isolation valve off and opened a hot tap to relieve the pressure. The cylinder immediately started to bang and started to pull the pipework into the insulation.

I have worked a lot with vented and unvented cylinders and understand that a negative pressure can cause a cylinder to implode, but I never thought an unvented cylinder would do this just by opening a tap on the next floor.

Has anyone else had trouble with unvented cylinders imploding? So far Gledhill say they are not aware of any issues with these but they have taken it back to inspect.

 

[Best]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

I haven't seen that happening with an unvented but have read about it happening. Apparently you are supposed to fit an anti vac valve where there is a risk on homes with different levels, which obviously is most.
I did see vented copper cylinders implode - one was when vent was frozen & hot tap downstairs was opened.
If the unvented cylinder had been fitted on ground floor that wouldn't have happened. If you fitted it, you might be responsible, especially if MIs state that it requires the valve fitted.

 

[townfanjon]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

Jeez, I would have another word with gledhill

 

[Best]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

Jeez, I would have another word with gledhill

Light stainless steel vessel designed for positive pressure but pressure of mains turned off & a tap opened at a much lower level = a hell of a suction on a sealed vessel

 

[townfanjon]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

Yep I know what you are saying but find it hard to believe . But the last few unventeds I have fitted weigh nowt , you can just about lift them with one hand

 

[russ01]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

I would have thought the fact that it is unvented, and therefore sealed, would mean that it could withstand a reasonable amount of negative pressure. What happens if the water board turn the water off when the hot tap is open? It is only a low 2 storey chalet house.

 

[Best]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

I would have thought the fact that it is unvented, and therefore sealed, would mean that it could withstand a reasonable amount of negative pressure. What happens if the water board turn the water off when the hot tap is open? It is only a low 2 storey chalet house.

Good point. There was a thread on this forum in fairly recent times about same problem.
I know that Telford say on their MIs to fit a anti vac valve where needed. If they are all that important you would think the manufactirers would supply one as standard.

 

[russ01]

Re: Gledhill Stainless lite unvented cylinder imploded when replacing valve to dishwa

I can't find anything in the instructions about fitting an anti vac valve, though it does have a specific procedure for draining down to prevent implosion including "holding" open the prv until the cylinder has drained.

I contacted Viessmann, as their cylinders are the same and made by Gledhill. The guy I spoke to said that he can't comment on any issues they have had, but around 18 months ago they started to supply anti vac valves with the cylinders from the factory. The pressure relief valves have changed to enable them to be left locked open.