Pressurised Hot Water Systems

[Stevekane]

A friend is doing up an old cottage, he opted to have an all electric mains presure domestic hot water system fitted and was aware that this is a specialist installation, the plumber has fitted everything and it all looks good except for the final connection to the cold feed and hot supply which are in position and ready to connect. Now the plumber has disappeared!
Apparantly the plumber had the correct certs to do the installation, so how do these things operate, is it enough that the fitting was done by a certified person who we could refer to or is there some form of registration,,can we do the final connection as ask building control to inspect the system? Anyone have any experience of this?
Steve

 

[Bingy man]

I’d imagine the regs are not to dissimilar to my trade ( gas engineer) in that it’s a specialist installation that will need to be tested and commissioned for safety and compliance purposes. In short -how do you know it’s been installed correctly and all the necessary safety controls are correctly installed. It will most likely not be passed by building control as the installation engineer is normally the same one who would test and commission it and then complete and submit the necessary documentation etc and also advise you the end user how it works . So contact the installer to complete the work or find another installer. You might though struggle to get someone willing to finish what he’s already started - good look

 

[Stevekane]

Many thanks Bingy, its certainly a bit of an odd situation, he is still trying to sort things out with the plunber and there is seemingly no reason why there should be any problems. Looking online it seems that these systems should have a yearly safety check, if he cannot get the plumber back would a way forward be to book a safety check with another firm, then at least the system would have been checked and tested?
Steve.

 

[Phil Pascoe]

Mine was fitted five years ago - it hasn't been checked nor was I advised to have it checked.

 

[Bingy man]

Many thanks Bingy, its certainly a bit of an odd situation, he is still trying to sort things out with the plunber and there is seemingly no reason why there should be any problems. Looking online it seems that these systems should have a yearly safety check, if he cannot get the plumber back would a way forward be to book a safety check with another firm, then at least the system would have been checked and tested?
Steve.

It’s certainly worth a few calls, just fully explain that the system is not complete and requires the final connections to be made. Honesty goes a long way with most installers.

 

[deema]

I have never understood why a pressurised system needed ‘special’ certification to install / maintain. It’s only at main pressure, and sure there will be air bladders at up to 2 bar, but that’s only car tyre range of pressures and then contained within a vessel.

 

[Bingy man]

I believe it’s down to the potential of what can go wrong with unvented/ thermal store systems if they are installed by an unqualified plumber or diy person who subsequently didn’t fit the safety controls and associated pipe work. On a regular vented cylinder if the boiler or immersion heater stats fail the water boils and goes up the expansion pipe and into the header tank -result extremely hot water but not much else. With unvented/thermal store if the safety components are not installed correctly or worse they are bypassed then the water will heat up and continue until it superheats and then goodbye house and anyone in the vicinity. Now these systems were not for me so I never did the extra assessments for the accreditation so I may not be exactly correct but rest assured it’s safety related and a lot of it was e u regs and just another way to make more money out of engineers and customers alike .

 

[Dee J]

I have never understood why a pressurised system needed ‘special’ certification to install / maintain. It’s only at main pressure, and sure there will be air bladders at up to 2 bar, but that’s only car tyre range of pressures and then contained within a vessel.

Temperature control fails and you have and uncontrolled heat source in a sealed tank of water. So - (a) need to make that unlikely to happen, and (b) if it doesn't shut down, make sure any release of superheated water and steam discharges safely. So, multiple stats, overpressure release and correct discharge arrangements. Some small tanks avoid yearly checks, but proper domestic mains pressure tanks should have yearly checks.

 

[deema]

Temperature control fails and you have and uncontrolled heat source in a sealed tank of water. So - (a) need to make that unlikely to happen, and (b) if it doesn't shut down, make sure any release of superheated water and steam discharges safely. So, multiple stats, overpressure release and correct discharge arrangements. Some small tanks avoid yearly checks, but proper domestic mains pressure tanks should have yearly checks.

Thank you, I’m surmising that’s really only applicable to situations where the tank is heated electrically by an emersion rather than with hot water from a separate boiler.

 

[Dee J]

Thank you, I’m surmising that’s really only applicable to situations where the tank is heated electrically by an emersion rather than with hot water from a separate boiler.

That gets confusing. So an all electric system with a separate electric boiler (on a vented loop?) heating a mains pressure tank, with no immersion (even for legionella treatment..). Seems a complicated arrangement. Surprised it's not just a vented thermal store with a mains pressure heat exchanger for hot water (which has a small enough mains pressure volume not to need licenced install and annual checks)

 

[Stevekane]

Many thanks for all your replies and Ive passed on the suggestions.
Its an intresting enough topic though, esp as I had no real idea of the regulations. My knowledge was limited to small electric undersink type heaters, which if they are less than 10ltrs (or possibly 15litres?) anyone can fit one, just plug and play as they say,,once you go over that size you have to have the special ticket. However in parts of europe a large electric water tank is a common thing, you could buy them at the local hardware shop and they hang on the wall in the bathroom, connected with flexables and with a cheap presure release valve screwed onto the inlet connection, no discharge arrangements, just whatever way the little nipple had been left pointing! Didnt seem to blow up etc, I guess if the stat failed it would just boil and discharge though the safety valve until the immersion burned out!
In this country, from the little I looked at re unvented electric water systems I wasn't sure if the yearly safety check was a requirement or a recommendation, I think it might be a requirement but lots of people seemingly don't get it done and don't know if they have too, no big fuss seems to be made about it so maybe its a case of ignorance is bliss!
Steve.

 

[Phil Pascoe]

My 200lt s/s tank of hot water is in the attic, so I would rather it didn't burst. There is a pressure device fitted that's vented outside. I've never heard a mention of getting the system tested.

 

[MikeJhn]

EU pressure tanks are normally over pressure discharged through a Tun dish to the outside of the property, pressure is set to normally seven bar, expansion tank is normally at two bar, incoming mains is nominally at three bar.

In France there is no special qualifications required to fit and no legal requirement for inspection.

 

[Bingy man]

Many large companies and probably a lot of smaller ones will inspect the hot water system as part of the annual boiler service by way of a visual inspection only , others will check the pressure in the expansion vessels and adjust as reqd . This information is not always passed on to the customer as their concern is normally the boiler.

 

[Spectric]

I have never understood why a pressurised system needed ‘special’ certification to install / maintain.

Because of a simple law of physics which is the expansion of water on heating. If you heat a volume of water in a sealed vessel that has no means of expansion then the pressure has to rise and it is this pressure than can result in the tank exploding. It is mitigated during normal operation by an expansion vessel which caters for the extra volume in the tank as it is heated but if that fails then you have a pressure / temperature release valve that should release the excess pressure if something goes wrong and this is the part that should be tested.

 

[MikeJhn]

The pressure vessels are just a sealed steel unit with a bladder inside and normally a Schrader valve at the top so they can be topped up, pressure inside is normally 2:3 bar, but its according to the pressure into the cylinder, most have a pressure reducing unit on the incoming water main to restrict this too 3 bar, as I said above the pressure release valve at the tun dish is set too 7 bar so the pressure vessel take a lot of this pressure before it lets go at the pressure valve. Legislation in France now requires a cold water mixing valve on the hot outlet to restrict the temperature at the taps.

 

[HOJ]

There is the issue with these systems that consumers are not generally familiar with, an unvented hot water system set at 3 bar pressure, the boiling point of water is + 130°C so under fault conditions water could instantly flash into steam when released into atmospheric pressure.