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Hot water system maintenance

Making a Splash

Hot water system maintenance


Hi everyone,


This is probably a silly question, but do hot water systems need to be serviced?


All of a sudden we are running out of hot water after a short period of use. 


We have only owned the house for 18mths and it doesn't look like an old system...I just don't want to wake up to no hot water one morning during winter!



Having an Impact

Re: Hot water system maintenance

What kind of system do you have @KingStreetReno? Gas, electric, solar? And is it an "instantaneous" system that heats water as you use it, or does it have a storage tank? 

Re: Hot water system maintenance

Hi @AHoy, it's a Rheem gas hot water system. I thought it was instantaneous as we never ran out of hot water, but all of a sudden we seem to be!

Re: Hot water system maintenance


Hi, if your Rheem is a smallish rectangular box then it's instantaneous, or if it's a large cylinder then it would be storage HWS.

I'm guessing it's instantaneous, & that the flame is being cut off by an out of adjustment or faulty gas regulator. Their purpose is to shut off the flame, if it thinks that the water flow rate is too low.

It may be as simple as tweaking the set screw, or it could've been brought on if you have hard water, & scale has built up in the water path of what looks like a cylindrical car radiator, the heat exchanger.

We had a gas instantaneous HWS, & I was able to just tweak the set screw, but if you're not confident, call a gas fitting plumber.

Another plan of attack, is to use your temperamental HWS as a kickstart to go Evacuated Tube Solar HWS. ; ) That's what we have now, & we love it.

Oops, just remembered, all HWSs have Pressure Relief Valves (brass body & a tin coloured lever which looks like a trigger), & they need to manually exercised every 6 months.

Building a Reputation

Re: Hot water system maintenance

Yes, as soon as I get some spare dollars, Evacuated Tubes are going on all my domiciles. Little bit expensive to start, but most efficient and easy to scale back in summer (PVC pipes cut in half to cover the tubes)

Also thinking about some HW storage, using older electrical HWS storage cylinders (for the insulated storage, not powered) and a little solar powered pump to get the water up to the tubes and back into the storage tanks.

You see these cylinders on the kerb often, I assume the elements have given out (calcified or otherwise) but usually still water/pressure proof, so they will be good storage (even if it's a pre heating condition).

For those that aren't sure of what I'm saying - If you get some heat into the water before the final heating, then your water heater isn't working so hard. Imagine if you have supply water temperature of 12 degrees and you want 65 degrees water at the end, then the tempreature difference is 53 degrees (water takes 4.2kW per kilo per degree to heat - so if you heat a kilo of water from 12 to 65 degrees it will take 222 kW of energy - if this is done in one hour, it will require 222kW/h - Maybe I'm going too deep with the theory??)

Anyways, even if your solar panels can increase the water in your storage (say 350 kilo's) by 30 degrees, then you save bucket loads of power required to get it to your required 65 degrees.

The main energy needs in a house/domicile is water heating and space heating (environmental heating for your comfort)

The easiest savings can be made with water heating.

Something else to keep in mind, your storage hot water system (HWS) must be a minimum of 65 degrees, but with the latest laws requiring a 'tempering' valve (which mixes cold water with the hot water) to finally supply water at a maximum of 55degrees, then inefficiencies are being built into the system.

This becomes quite deep and requires some deep understanding to get a grip on what is happening in the HWS - so some 'preheating' of the water is quite valuable.




Community Manager
Community Manager

Re: Hot water system maintenance

Thanks for sharing @Kev.


You might also be interested in this previous discussion on Workshop - Options for replacing gas booster on solar hot water system



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Finding My Feet

Re: Hot water system maintenance: Formula for amount of power to heat water.

Hi Kev (Aug. 2017), I think you're a little "out" with the amount of power required to raise the temperature of water... the amount you've quoted (222kWh) would have your example water quantity vapourised in a fraction of a second!

A formula that can be used is: "To calculate the kilowatt-hours (kWh) required to heat the water, use the following formula: Pt (kWh) = (4.2 × L × T ) ÷ 3600.   Pt is the power used to heat the water, in kWh.    L is the number of litres of water that is being heated and T is the difference in temperature from what you started with, listed in degrees Celsius."

The approximate power to heat 1 litre (1 litre of pure water weighs 1 kilogram) by 1 degree Celsius is 1 Wh (watt/hour) (0.001kWh).

So, as an example, an electric hot water storage tank that holds 400 litres will need just over a total of 23kWh of electricity to heat the 400 litres from (e.g.) 15DegC to 65DegC ( 50DegC rise).

This size tank typically has a 4.8kW heating element. This means the tank will draw power for nearly 5 hours to achieve the heating required in the above example. This fits with the typical "Off-Peak1" electricity tariff that is usually available some 6 hours out of each 24 hours. (Sydney Aust.)

Community Manager
Community Manager

Re: Hot water system maintenance: Formula for amount of power to heat water.

Thanks for joining in the discussion and sharing your knowledge @Dal. It sounds like you have a lot of experience and expertise that you can share with the community. I trust you'll also get plenty of helpful advice and inspiration for your projects from our clever and creative members. 


Feel free to post whenever you need a hand or have something to contribute. We look forward to seeing more of your posts soon.






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Kind of a Big Deal

Re: Hot water system maintenance: Formula for amount of power to heat water.

Continuous hot water systems may require professional servicing if there is a fall off on the hot water. however please check the following.

1. Do you get the same hot water drop out in the kitchen or does it stay steady? If yes check laundry and other taps, if symptoms the same continue to no. 3. If no continue to no. 2
2. Have your regulator checked. Is it auto transfer or manual transfer. Some auto units fail and only switch halfway when 1st tank is empty. Providing minimal gas and makes the hot water unit think your running out of gas. Switch has failed? replace with more up to date models. If not continue to no. 3
3. Distance to shower and exposed copper pipes. Sometimes distance plays a part and you may need to put lagging on the copper pipe to provide insulation. However if the symptom has only recently arisen there is one more port of call and that is your tempering valve. It could have failed and may be excessively cooling your hot water, turning the tempering valve to full hot should eliminate the cause, if so then you know it has failed and can be replaced. Beware that a faulty tempering valve can cause excessive hot water to flow though your pipes and scald the person using hot water! Please be safe when testing, council regulations in your area may require a tempering valve and please note that a registered plumber may be required to do this. If this still fails then step 4 is your last stop.
4. If the Rheem unit is more than 10 years old it may be time to service it. 1300 556 036 install a rheem...install a rheem...!

I am a Bunnings team member. Any opinions or recommendations shared here are my own and do not necessarily represent those of Bunnings. Visit the Bunnings website for assistance from the customer service team.

Just Starting Out

Re: Hot water system maintenance


Had a power cut lately? If so, maybe your controller needs to be switched back on.

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