Pressurised vs loft tank CH systems?

There is always a little confusion over what is pressurised in a heating system. I don't disagree with any of the above comments. Just thought I would add my personal comments about my system and why I choose it to be as it is. House built in 1989 with standard regular boiler and two headers one for primary heating loop and one for immersion hot water feed.

When I upgraded I choose to fit a seperate pressurised hot water cylinder. Advantages no pumps for shower and mains cold water pressure delivered hot water. In the event of boiler failure I can turn on the immersion heater and still have hot water. disadvantage the pressure vessel will fail at some point between 1-3 years and that is a routine change out. (look at the number of pressure vessels screwfix sell to see this is a good turn around. I am prepared for this minor disadvantage as all other benefits outweigh it.

The boiler is a regular boiler it's sole job is to heat water with no added complication within. Separate standard pump to circulate, standard zone valves to divert water to where required. I split upstairs and downstairs and added workshop loop and underfloor heating. All these things are within my control and need no specialist intervention. I kept the open vent header feed for the boiler and not pressurised because I don't want to find micro leaks that may be no issue currently (although confident there are none) don't want the hassle of topping up when pressure lost. don't want the hassle of an internal special pressure vessel within a "system boiler" needing specialist replacement. Possible negative header tank washer every ten years but system will still work with overflow fault indication, simple. I don't regard freezing of tank or leaks in loft as a probability (although always a risk) and are covered with overflow tray to outside.

Combi boiler I would never consider as have had experience of them and a failure of any aspect means both heating and hot water are likely to be lost, and there are more specialist parts blenders, sensors etc. I found there is always an inconsistency in the hot water delivery and can be affected by draw off elsewhere in the property.

That said combis do have advantages they are quick to fit and make the installer more money, regular boiler and cylinder will cost more to fit. If space is an issue then clearly it can have it's advantages. It's the individuals choice but understanding fully why the choice is made is key to a happy outcome which will always be a compromise of circumstances.

Alan

That doesn’t sound right.

When we had our boiler installed a few years back the installer specifically asked me if I wanted hot water “on demand”. He explained that the boiler would come on as required to keep the water hot in the system. I told him not to bother and even so it doesn’t take long for the water to get hot.

Only heating water as we need it rather than heating it and storing it in a tank definitely lowered our gas bills.

By the way. Thanks for this thread. I've just done some checking on the screwfix website and realized that things have moved on in the 28 years since I rebuilt the heating system.

I had been thinking that I needed to get a combi boiler or booster pump in order to satisfy SWMBO's desire for a high pressure shower. I see that the world now includes high pressure indirect hot water cylinders. So I can keep the existing boiler and HW pipework, replace the cylinder and get mains pressure hot water.

Luckily, our council tip still accepts asbestos cement, so I can dispose of the cold water tank with no issues.

It is interesting that no-one has mentioned the added complications of including solar heated hot water supply into the discussion. It almost inevitably requires a twin coil heat exchanger, one for regular boiler supply, the other for solar input which has it's own pressurised system treated with propylene glycol to lower the freezing point of the circulating fluid.

We installed a Navitron 20 tube system, rated at 1 Kw, which was commissioned in June 2010. Since then it has supplied 13400 kwhours of water heating and saved about £600 overall on the gas bill. One tube lost vacuum about 2 years after installation, I had spares to hand and to change it was about 20 minutes work while the rest of the panel was still working.

It is not just a summer working system, there is still solar energy of value in the winter months which saves the boiler some of the grunt work.

Brian

Southampton water is extremely hard and I have had a water softener for a number of years. Very well worth while! When we last replaced the boiler I kept the loft cold water tank (supplying the HW cylinder) fed from the softener as it made it easy to arrange a softened cold feed to the upstairs bath and shower pump. Unfortunately the geometry made it impractical to run the downstairs electric shower from the softened supply, but it doesn’t get used as often anyway.

Niall