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How to solve the problem of a direct gas water heater or combi boiler

Updated on March 10, 2011

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Love them or hate them, they're here to stay

You might love. I hate them.

My experience of directly heated gas water heaters or combi boilers has not been.... enjoyable. Maybe I haven’t met the right one. Maybe they were all out of date appliances, but whatever, I’ve never been a fan.

We had gas water heating in the house where I lived, but it was indirect heating – a coil of copper tubing from the gas appliance acting as a heating element inside a large hot water cylinder. The cylinder of water was at an even temperature.

No control

My first experience of direct water heating was mid 1991 when I visited a friend in Spain. The directly heated gas water heater supplied the kitchen and two bathrooms/showers. They’d disposed of an electrically heated water system because of running costs. Apparently most of their neighbours were having electrically heated systems replaced with gas as well. In fact, electrically heated water tanks could be seen on all the refuse tips.

I recall standing in the shower on the first evening, trying to adjust the temperature. Uggh! It either scalded the skin off my back or was too cold. Nothing seemed to correct the imbalance. My wife gave up. Our hosts had no problem – they used a bath. The highs and lows were mixed up and they saw nothing wrong.

Just blast it out

It seemed the heater regulated itself by being either being on, or off. No high, low, or medium – the AVERAGE temperature over a period was correct, the instantaneous temperature was anyone’s guess.

We visited each year and discovered the only way to maintain some semblance of control was to have the water on full bore in the wash-hand basin, as you were taking a shower – never mind about wasting water in a country full of drought – just blast it out.

My next experience came in the UK after selling our property. We rented a flat for a short period until we were ready to move to a new home. It too had a direct water heater – similar problems – I hated the damn thing to distraction.

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When we moved into our villa in Spain and ordered a gas central heating installation, we found they supplied no such thing as indirect water heating, only a combi boiler was available – direct water heating. My heart sank.

Never one to be beaten, I sat down and worked out a system to get over the problem. I mulled it over and decided that a mixing chamber was the answer.

Let blasts of hot and cold water from the gas heater go into a large chamber and mix before being used – the average temperature would be correct – but, what if the water were standing in the chamber for hours without being used? In fact, it would happen every single day. The first draw of water from the system would be cold or at least cool, until the correct mixing took place – potentially a whole tank of water would be wasted trying to get the temperature correct.

A solution to the problem

The answer - an electrical heater and thermostat to keep the water temperature topped up. It would also have the advantage that if gas went off – it had electrical backup – if the electric went off, the storage tank would do it’s mixing whatever – not quite as efficiently – but great stuff.

The practical application was evident – find a suitably sized electrically heated water tank with thermostatic control – of which there are numerous on the market – or refuse tips if need be – but feed it from the hot water from the outlet of the gas water heater instead of the normal cold water supply (but have a valve arrangement to switch over to cold water supply – just in case it’s needed).

Evenly regulated

The result – perfection!

We now have the cheapness, low cost, and convenience of a directly heated combi boiler - yet an evenly regulated temperature.

It's only topped up from the electrical heater when it starts to cool – and it provides built-in backup for water heating.

What more could be wished for. Topping up with electrical heating doesn’t cost a fortune because the tanks are very well insulated, it only comes on every now and then. The main heating is from gas – great stuff!

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