Leaking Ariston 2kW Water Heater.

Excuse my late entry to this post. I’ll start to say that I'm less familiar with current regulations than I used to be some years ago as I’ve not dealt with it for some time. 

That YouTube video for fitting the Ariston Andris Lux unvented water heater is helpful but for reference the UK manual for the water heater is at 42.0.01.06166.00 copertina (ariston.com)

Ariston indicate that:

IN ORDER TO FIT AN ARISTON ANDRIS LUX IT IS GOOD PRACTICE AND SOMETIMES MANDATORY TO INSTALL ONE OR SEVERAL OF THE FOLLOWING KITS 

Kit A is an Expansion Vessel & Non-return Valve

An expansion vessel is a device that takes up the expansion of water in the domestic hot water system when it is heated. This prevents build-up of excess pressure. The non-return valve prevents backflow of expanded hot water in to the cold water main.

Kit B is a 3.5 Bar Pressure Reducing Valve

The maximum cold water inlet pressure designed for the Andris unit is 3.5 bar therefore this pressure reducing valve controls the water to not exceed this limit.

KIT C is a Discharge Tundish

In the event that the hot water system over pressurises, the highly pressurised water is discharged via the 6 bar pressure relief valve and the tundish serves to visually indicate that this discharge is occurring.

Ariston indicate as expected, and like many electrical comments on this Forum that the installer needs to be competent.   

The drawing on the bottom of page 12 shows what an installation could look like by way of a pressure reducing valve (optional depending upon circumstances), non return valve (I thought NRV’s were mandatory under UK water regulations where back flow into the water suppliers mains is not allowed for contamination reasons and why we have air gaps in taps to basins and in ball valves etc), expansion vessel and then pressure relief valve before the water heater.  The guidance of which of those kit items are given at the bottom of page 19. 

As to the question of can they blow up, yes they can if not installed and maintained correctly by a competent person.  I have somewhere but cannot find at present, an old Defect Action Sheet (DAS) from the Building Research Establishment wherein an unvented cylinder had exploded, taking out the side of a timber framed building where a lack of competence was identified in both installation and maintenance stages.  It was a much larger cylinder than this 10 litre type but the principle remains the same, just the size of the failure may differ.  

In the situation posed, it looks like the customer installing it in their own home was not competent and I would suggest advising them to read the manufacturer’s instructions, if they don’t have the skills and equipment to install it correctly then  they should employ someone who does, and walk away.

Some older unvented under sink water heaters (I’m not sufficiently aware of all products on today’s market) used their own manufacturers matched taps to allow pressure release and some years ago I twice caught clients employing plumbers to replace a dripping mixer tap that was matched to the under sink unvented water heater (Heatrae Sadia if I recall) with a new standard mixer tap that would not drip.  That would have prevented the pressure relief from expansion with a possible leak or worse.  Plumbers who were not competent in unvented systems were involved. 

Paul

Excuse my late entry to this post. I’ll start to say that I'm less familiar with current regulations than I used to be some years ago as I’ve not dealt with it for some time. 

That YouTube video for fitting the Ariston Andris Lux unvented water heater is helpful but for reference the UK manual for the water heater is at 42.0.01.06166.00 copertina (ariston.com)

Ariston indicate that:

IN ORDER TO FIT AN ARISTON ANDRIS LUX IT IS GOOD PRACTICE AND SOMETIMES MANDATORY TO INSTALL ONE OR SEVERAL OF THE FOLLOWING KITS 

Kit A is an Expansion Vessel & Non-return Valve

An expansion vessel is a device that takes up the expansion of water in the domestic hot water system when it is heated. This prevents build-up of excess pressure. The non-return valve prevents backflow of expanded hot water in to the cold water main.

Kit B is a 3.5 Bar Pressure Reducing Valve

The maximum cold water inlet pressure designed for the Andris unit is 3.5 bar therefore this pressure reducing valve controls the water to not exceed this limit.

KIT C is a Discharge Tundish

In the event that the hot water system over pressurises, the highly pressurised water is discharged via the 6 bar pressure relief valve and the tundish serves to visually indicate that this discharge is occurring.

Ariston indicate as expected, and like many electrical comments on this Forum that the installer needs to be competent.   

The drawing on the bottom of page 12 shows what an installation could look like by way of a pressure reducing valve (optional depending upon circumstances), non return valve (I thought NRV’s were mandatory under UK water regulations where back flow into the water suppliers mains is not allowed for contamination reasons and why we have air gaps in taps to basins and in ball valves etc), expansion vessel and then pressure relief valve before the water heater.  The guidance of which of those kit items are given at the bottom of page 19. 

As to the question of can they blow up, yes they can if not installed and maintained correctly by a competent person.  I have somewhere but cannot find at present, an old Defect Action Sheet (DAS) from the Building Research Establishment wherein an unvented cylinder had exploded, taking out the side of a timber framed building where a lack of competence was identified in both installation and maintenance stages.  It was a much larger cylinder than this 10 litre type but the principle remains the same, just the size of the failure may differ.  

In the situation posed, it looks like the customer installing it in their own home was not competent and I would suggest advising them to read the manufacturer’s instructions, if they don’t have the skills and equipment to install it correctly then  they should employ someone who does, and walk away.

Some older unvented under sink water heaters (I’m not sufficiently aware of all products on today’s market) used their own manufacturers matched taps to allow pressure release and some years ago I twice caught clients employing plumbers to replace a dripping mixer tap that was matched to the under sink unvented water heater (Heatrae Sadia if I recall) with a new standard mixer tap that would not drip.  That would have prevented the pressure relief from expansion with a possible leak or worse.  Plumbers who were not competent in unvented systems were involved. 

Paul