Unvented cylinder vs combi-boiler, plus/minus power shower

[ElleDubloo]

We're moving to a 1920's detached house, which needs lots of renovating including new bathrooms and a new boiler. I can't decide what type of boiler to get, as an absolute newbie to houses and things.

As I understand it...

Unvented cylinder = water comes direct from the mains, cold water to taps comes off, then the rest goes into a boiler which supplies hot taps directly at mains pressure. Benefits include hot water at high pressure, able to run multiple taps/showers, powerful showers, quite energy efficient. Disadvantages include high cost of installation, potentially dangerous, needs annual professional maintenance.

Vented cylinder = water is stored in a tank in the loft before coming down to the cylinder and getting heated. This is what the house currently has, but the water tank in the loft is leaking and causing damp, so needs to be replaced. Am I correct in thinking there's no point getting a new vented cylinder as the alternatives are all better?

Combi-boiler = very energy-efficient and space-saving, cheaper to install and does not require annual maintenance. However, cannot supply hot water to more than one tap/shower at a time.

Our plumber has suggested an unvented cylinder, because we like hot powerful showers. But I'm put off by the high cost (and ongoing maintenance cost). What about having a combi-boiler and a pump for the shower (i.e. power shower)? Will it be as effective or better? What are the other pros and cons?

Thanks in advance!

[HelenF350]

I was always under the impression that you couldn't have a power shower with a combi as there is no tank so the maximum water pressure cannot be increased? We have an unvented cylinder. Can't comment on maintenance as we have only had it 6 months but the water pressure in the shower is way better than it was with the previous power shower!

[PigletJohn]

You mention bathrooms. A combi is not very suitable if you have more than one.

An unvented cylinder can give you unsurpassed hot water.

As there is no cold storage tank, you need a good flow from the watermain. Fill a bucket at the kitchen cold tap (and the garden tap and utility room tap, if you have them). Time it to full. How many litres per minute do you get?

Unvented cylinders are less dangerous than kettles. Unvented cylinders have several safety devices to prevent them overheating or going over pressure, and the annual check is to verify that they are still present and working. It can be done when your boiler is serviced so not an expensive job. The boiler is less complicated than a combi so has less to go wrong, and is likely to last longer.

With any cylinder, you can add an immersion heater (or preferably two) so that you will have hot water even if the boiler is out of action.

[ElleDubloo]

Thanks both of you, that's very helpful. As you can tell, I know next to nothing about plumbing but I'm learning!

PigletJohn, I'll run the taps when we get the house (we complete in just over a week). What's a good flow rate? What do I do if there isn't a good flow rate from one/all of the taps?

[PigletJohn]

Less than 20 litres per minute is unsatisfactory for a combi or an unvented, but not if you have a loft cold water storage tank.

You get out your spade and dig a trench across the front garden, to lay a new, larger plastic water pipe out to the watermain under the pavement. Digging flowerbeds is easier than digging concrete.

If the house is old and the pipe is lead it will be especially worthwhile, and (ask the water co to test the water for lead content) you might get a lead replacement subsidy.

If the house is old and the pipe is iron it will be rusty and either already leaking or planning to start.

You will be astounded at the difference a new pipe can make (subject to full-bore stopcocks, valves and tap connectors)

[ElleDubloo]

That sounds good! (though expensive... might need to wait a couple of years for that project...)

[superram]

Don't wait two years do it now, complete pain to do it afterwards as you will need to rip up flooring in the house if pipe is under floorboards

[lolalotta]

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