Your hot water geyser can explode!
In this article, I will describe the typical basic requirements of a sound, modern high pressure, horizontal installation. The following description relates to a modern high pressure (400/600 Kpa) system typically made by Kwikot South Africa.
Horizontally mounted 150 or 200-litre units are by far the most common in modern domestic installations. Less common are old low-pressure systems (100kpa) open pipe or “Latco” type systems. Be aware that the parts are NOT interchangeable between the two distinct systems – High pressure and Low pressure! It is possible to remove an old low-pressure system and replace it with a modern high-pressure system, however – you buy a new high-pressure geyser and install it according to the current specification. Vertical geysers are also common.
Safety tips for hot water geyser installation
Here is what you should see – in no particular order:
The most obvious thing that you should notice right away. The hot water geyser sits in a tray made of plastic (often red) or tin plate. I prefer the plastic ones. They don’t leak. Since June 2001, the drip tray is not optional – its got to be there and there has to be a drain pipe for it! The drain is a 50mm PVC waste pipe that drains the tray by piping the water out of the house. I have seen many drip trays installed without drains! If your installation pre-dates June 2001 you may want to get a plumber to look at it. There is a fair chance that there is no drip tray.
The next most noticeable feature would be the vacuum breakers. These are mounted at the end of a 30cm length of pipe. The two vacuum breakers stand vertically about 30cm above the hot water geyser. These important breakers prevent water from syphoning out the geyser when the cold supply is stopped.
The other function is to prevent a vacuum from forming in the tank and collapsing it. It can be argued that this is the primary function, but I don’t see it as such. Remember those vacuum breakers are a reasonably new requirement – there are still thousands of old HP systems out there without vacuum breakers and I am yet to see one collapse. Just because I haven’t seen it doesn’t mean it’s not happening! It is also more likely to happen in a multi-story building because the syphon can draw a more powerful vacuum. High-pressure systems must have vacuum breakers!
Shut Off Valve
A shut-off valve (tap) on the cold water side. The cold water side is the side that directly connects to the drain cock and enters the geyser at the bottom. After the shut-off valve, you would normally find a Pressure Control Valve (PCV). There are a number of different types made of brass or plastic. You should notice an overflow pipe connected to the PCV that leads to the outside of the building. This is where the PCV releases pressure and this is the pipe that often drips. It may be mounted on the outside at the entrance of the water supply into the home. Sometimes it’s in a little plastic box outside.
A safety valve, known as the Temperature and Pressure safety valve (T&P Valve) mounted on the hot water geyser towards the top, often on the opposite side to the drain cock. Never mess with or repair this vital component. This valve should have a metal (copper or steel) pipe connected to it and the pipe must lead directly out the building. This vent pipe is an important safety feature of the whole system. It must be copper or steel. The pressure rating on this valve must match the pressure rating on the geyser. The T&P valve is the least optional component – it has to be there!
The roof trusses must support the weight of the geyser and tray. A minimum of two supports under the ‘feet’ of the geyser in the tray. If it looks shaky have a plumber check it out. Nothing like a full (hot) geyser on the kitchen table to get everyone talking!
A requirement is that electrical isolator switch is installed within 1 metre of the hot water geyser. However, this was not a requirement on old geysers, but it’s worth fitting one. Furthermore, the geyser has to be earthed! I have seen many geysers with the earth wire unconnected. Earthing of all the copper pipes must also be earthed and bonded to the geyser earth. This is not a trivial precaution! Get a qualified electrician to check your installation if the bonding is missing or looks incorrect. Electrocution in the shower is always unpleasant!
There should be a cover protecting the thermostat and element. There are essentially only two primary thermostat types – the modern round “Kwiktherm” in newer Kwikot geysers and the VK (rectangular block) type in older geysers and in some newer non Kwikot units.
The hot water geyser may be fed (cold water) with polycop (plastic) pipe – up to the shut-off valve, but the pipe into and out of the geyser must be copper or galvanized steel. The PCV and T&P vent pipes also have to be steel or copper, especially the T&P vent. Furthermore, the hot water side should be copper, steel or suitably rated (70°C) plastic or composite pipe. Note that you must have at least 1 metre of copper/steel pipe out the geyser – you may not connect plastic (composite) pipe directly to the geyser.
As above, the PCV and T&P must be made of copper or steel, particularly the vent out of the T&P valve. In the event of the T&P (safety) valve releasing, the water coming out is likely to be very hot! Furthermore, a polycop pipe will melt! It will either spill water into your ceiling space or into your geyser tray! The regulations require a metal PCV valve. I have seen a number of installations where the installer has simply run a short length of 22mm copper into the drip tray with the idea being that the T&P can vent directly into the drip tray. This is a very bad idea because the hot (100°C+) water/steam melts the drip tray and the PVC drain pipe.
Note that water enters (cold) and leaves (hot) from above the geyser top as shown in the diagram below. The PCV (pressure control valve) is typically before the geyser. The cold water piping forms a loop before the cold water flows down into the hot water geyser. This is quite important because it forms an anti-syphon loop that prevents the geyser from draining back through the inlet in the event of a water supply failure. If you get hot water coming out your cold taps when the water supply fails then this is not working correctly. Get a plumber to come and have a look at it.
Lag the pipes into and out of the geyser. This is important if you have ‘Think Pink’ or ‘Isotherm’ ceiling insulation. The reasons are twofold: You lose heat through the unclad hot water pipes and all the pipes are more prone to freezing (and bursting).
In addition, there must obviously be no signs of water! Any water lying in the drip tray is a sign of trouble.
I have described a typical, modern high pressure (400-600 Kpa) system which is the most common type in South Africa. In addition, much of the description still applies although vertical geysers are different. However, low-pressure systems (100kpa), although fairly uncommon, are significantly different.
The same general rules apply as above, but the outlet and T&P valves must be at the very top of the geyser. Furthermore, the element and thermostat must always be at the very bottom. Allow enough room underneath to allow the changing of the thermostat and element. There is a greater temperature differential in a vertical geyser, the thermostat is a couple of degrees cooler than the outlet water. I tend to turn the thermostat down a tad more for this reason.
from an article by Blockbuster Plumbing in Home-Dzine