Unvented Systems 101:

Want a brand new and shiny system in your house?
Well this is the one to go for. It’s very similar to a traditional vented system (please see my other blogs for more info) but there are no tanks in the loft thus saving space and runs off mains pressure therefore in theory giving you a better shower experience and toilets that fill up quickly.
An unvented system is basically made up of 2 parts. The Boiler and The Cylinder.
1. The Boiler.
Because high water pressure and high temperatures don’t mix very well there is a safety feature that if the pressure gets too high a valve opens and all the water will gush out to safe place. This is called the PRV or the Pressure Relief Valve. This is connected to the Pressure Relief Pipe which you’ll normally see clipped to an outside wall. If this goes off and you see water dripping from the pipework then call us a there’s a problem with your heating system.

A system boiler will have a Pressure Vessel inside the casing and a converted regular boiler will have the pressure vessel somewhere outside normally close to the boiler. It’ll look like a large red balloon… made out of metal.
Its controlled like every other heating system with a programmer, room thermostat, cylinder thermostat, zone valves etc etc.
The boiler directly provides heating for the radiators and indirectly provides hot water from…

2. The Cylinder.
An unvented hot water cylinder has to be made for purpose. You can’t use a normal cylinder as it hasn’t been pressure tested or have the correct safety controls on.
At 100 degrees C water will expand by 5 times its volume. Just boil a kettle and see what happens. Check out this video from some nutcase Americans to see what happens when you play with the safety devices or use an installer who is not properly trained or qualified. https://www.youtube.com/watch?v=ekEHfihiNz4
Whilst we’re discussing heating engineers make sure that they’ve got a G3 Certificate. This means they know what they’re doing, can self-certificate the installation and you’ll have a great system that will last a long time.
There are 2 types of unvented cylinders. Both work on the principal that when water is heated it expands. They both need some sort of vessel to hold the expansion of the water.
1. Megaflo.
These are quite clever. They have an internal air baffle that acts as a pressure vessel. The vessel may need to be ‘topped up’ every few years. Because the baffle is inside it saves space so you can situate it in more places. These cylinders currently have a Lifetime Cylinder Warranty.
2. Gledhill or others.
These have an external pressure vessel. Gledhill in particular has a 25 year warranty and works out relatively cheap as any extras like the pressure vessel itself and the immersion heaters are all included in the pack.

Something important to consider.

If you are seriously thinking of having a pressurised system installed mae sure that your cold water mains pipe is up to the task. You may need to have the pipe from the street to the house sized up to be able to give you the pressure you want. And this will involve some digging and at least £1000 on top of your original budget.
To get the best possible performance you will also want to change the hot and cold pipes inside the house to a larger size to get the best possible flow rate and have a true Power Shower.

If you have any questions don’t hesitate to contact us.

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