Building Construction, Renovation, Maintenance & Advice

Demand Gas Hot Water Heaters

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"The Hot Water Twostep"

It’s a real pain isn’t it? You find a towel and step into the shower and turn on what you think is the hot water tap (that nice landlady promised you there was hot water) and the water flows - cold. You turn the shower nozzle away and cower in the shower trying to avoid getting wet until you find warm water. You wait. You feel that two hours pass and still the water is cold. Must have been the other tap so you turn the first one off and the other one on. Once again you cower while cold water flows for what seems like a further couple of hours. The water is still cold.

Try the first tap again. Cower for another eternity and just when you are about to give up boiling hot water suddenly issues forth from the shower head and you jump around trying desperately to avoid getting scolded or stepping in the expanding pool of hot water while trying to reach the hot tap to turn it off. You manage to close the offending orifice and, with a sigh of relief and a shrug of resignation, you regain your composure.

Round 1 - Plumbing 1, You nil.

“Oh well at least I found hot water.” The words pass through the neurones of your brain as you try to convince yourself that you have made progress towards that elusive holy grail of bathroom activity - a nice shower in water of just the right temperature.

Don’t get too smug this infernal system is not done with you yet.

You start again, this time you think you will be clever and beat this system. You turn on the cold water, only half way this time and then turn on the hot. Once again you cower and wait, - nothing. You turn the cold down a bit then after a delay Eureka! hot water but it is still far too hot to get into. You turn the cold on a bit more, after the familiar delay it cools a little but is still far too hot. More cold, another delay and, feeling brave, you step into the water. After two seconds the heat is too much, your head and shoulders are burning like a well cooked lobster so you turn the cold on a little more. You wait the usual delay and suddenly freezing cold water is falling on your head. Your day is starting to drain of pleasant emotions as words on topics such as the contents of a septic tank or urging sexual activity between people born out of wedlock tumble from your mouth and you make a dive for the taps.

Round two - Plumbing 2, You nil.

You grit your teeth. You are not going to let some primitive technical installation created by some primeval lifeform destroy your demeanour and your day. You try another approach. Mumbling confrontational words designed to scare and subdue your aqueous adversary you perch on the side of the shower and turn on the hot water to full. You wait, eventually it flows hot. So far so good. Now stealth is the strategy, you turn on the cold very, very slowly, you’ll sneak up on it so it won’t notice. The water gets cooler ever so slowly then, just as you are considering you might claim victory and step into the water flow the water suddenly goes cold. At this stage you start to speak in tongues uttering words you didn’t even know that you knew.

Round three - Plumbing 3, You nil.

Things start to go downhill .………………

Round twenty four - Plumbing 24, You nil.

Not a lot of progress really and sanity is starting to fade. You look around for a window or an orifice of some kind. There must be a spyhole somewhere behind which some psychopathic landlady is cackling in delight and taking out her deep seated hatred of all living things …………….

Round forty six - Plumbing 46, You nil.

You decide to give up this ridiculous idea of a hot shower. Huh, you didn’t really want one anyway. You turn on the cold water and, your heart being set on a somewhat warmer experience, the water seems colder than ever. You brace then throw yourself into the flow of water and dance about rubbing yourself as briskly and quickly as possible. You turn off the taps, grab a towel and exit the bathroom glad to be away from that possessed plumbing.

Plumbing - game, set and match.

The cause of all this is, of course, a gas water heater.

Gas Water Heaters

Gas water heaters are very popular in Indonesia (although the vast majority of people in this country don’t have hot water) and in other countries too notably Australia where they make up 50% of all new water heater sales.

Storage and Demand Water Heaters

They come in two basic types. The first are gas “storage” water heaters which, like solar, air conditioner and most electric water heaters, heat a tank of water which is stored ready for use.

The second type are of more interest to us today and are “instantaneous” or “demand” water heaters (also known as multipoint heaters, tankless heaters, geysers or ascots). These heaters heat the water “on demand” as it is needed.

Geysers (not to be confused with geezers that tend to lean against the bar chainsmoking and coughing into their beer) have been around for many years. Early models In Britain were often mounted on a wall in a confined space such as over the kitchen sink and, owing to their idiosynchratic behaviour, had rather a habit of scaring people (come to think of it both kinds of Geysers do that).

There have been a lot of technological advancements and these days gas water heaters are a lot safer than in the early days although the same safety considerations still apply but we’ll come to that later.

Gas water heaters are very popular and understandably so. They are cheap, quick and easy to install, they are very compact don’t take up much space, they heat the water as it is needed, you never run out of hot water and from an environmental point of view are efficient when compared with electric heaters. The downside here in Indonesia is that you have to keep changing the gas cylinder.

How do they work?

Demand gas water heaters vary in size but all follow the same basic design. Inside the outer casing is a metal heat exchanger in the form of a vertical cylinder around which a heating coil, a spiral of pipe, rises. This cylinder finishes at the top in a flue. At the bottom in the centre of the heater is a circular gas ring with a series of gas jets forming a ring of flame.

The cold water enters at the bottom of the spiral and is heated by the heat from the gas ring as it rises up the cylinder and is hot by the time that it leaves the top.

When not in use the gas is turned off. When you turn on a hot tap water starts to flow through the heater which senses the flow of water, turns on the gas and electrically ignites it. The heater roars into action. As soon as you turn the water tap off the water flow stops and the gas flow is cut off.

Controls on the front of the heater allow you to adjust the gas flow and the size of the flame and thereby the output temperature of the water.

Older models had a pilot light which burned permanently ready to ignite the gas jets when the heater switched itself on. Pilot lights had a habit of blowing out in a strong draught. These days the pilot light is gone. The heater is connected to an electrical supply and the gas is ignited with an electric ignition. This is the main reason why modern heaters are far safer than the geysers of old.

Now we come to a critical element in the gas water heater’s design. If the water flow is too low to carry away the heat the heat exchanging coil will overheat and be damaged so, to safeguard the heater, the water flow is monitored and if it falls too low the gas is turned off.

Gas water heaters are very efficient and can produce very hot water so when you are in the shower you only need a little hot water to mix with the cold (particularly in Bali). When you turn the hot tap down the flow through the heater may not be enough and the gas heater switches itself off.

When people have problems with their gas heaters they often make the mistake of turning the gas up to maximum to try and solve the problem. The hotter the gas setting the more water you need to flow through the heater to stop it turning itself off.

So, if your heater keeps switching itself off while you are trying to shower the starting point is to turn the heater down.

There are other common problems with gas demand water heaters. Many people have low flow rates through their gas water heaters due to the small diameter of pipe in the heat exchanger coil.

If you have hard water the inside of the heating coil very easily scales up with calcium which, due to the heating effect, is deposited inside the pipe. This reduces the diameter of the pipe and reduces the flow of water through the heater - a very common problem but it can be fixed.

Another more complex problem relates to the difference in the water pressure in the hot and cold water pipes to the shower. Very often the water pressure is lower in the hot water system due to restrictions in the pipe through the water heater. Unequal pressure in the shower mixer tap may result in higher pressure water in the cold water pipe pushing back up the lower pressure hot water pipe slowing down the flow and switching the heater off.

Finally some words of warning. Gas heaters should be mounted outside if possible and in a well ventilated space. They should not have anything flammable above the flue and you certainly should never put anything on the top of them.

They are also not something that you should attempt to repair yourself. These heaters can hang on your wall and quietly and efficiently run for years with little attention. However if you do have problems or one of those tedious bathroom experiences you can always tear it off the wall and, lifting it over your head, throw it over the garden wall with the customary cry “take that you ignominious piece of dried gorilla snot.” Game, set and match to you.


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Copyright © Phil Wilson 2010
This article or any part of it cannot be copied or reproduced without permission from the copyright owner.

9 December 2017 Copyright © Mr Fixit,
Jl Bypass Ngurah Rai, Gg Penyu No 1, Sanur, Bali 80228, Indonesia
Telephone: +62-361-288-789, Fax:+62-361-284-180