how does an unvented cylinder with boiler work for dummies please

Lexie_M

looking at buying a property (4 bed 2 bath) which has a boiler with a megaflo unvented cylinder. I have never encountered this. Can someone please explain how it works? they told us it's hot water on demand but I can't see how that would work with a hot water cylinder unless you have it on constantly.
Also, is the tank used for both heating and hot water or is the heating straight from the boiler? do I always need to have hot water in the tank in order to get heating and hot water?

knightstyle

DD had this in her last house, built 2008. She had no end of expensive problems with it, replacing various valves, two expansion tanks etc,
My advice would be to avoid buying or budget for replacing with a standard system with a tank in the loft.

BoxerfanUK

knightstyle wrote: »

DD had this in her last house, built 2008. She had no end of expensive problems with it, replacing various valves, two expansion tanks etc,
My advice would be to avoid buying or budget for replacing with a standard system with a tank in the loft.

With respect. I couldn't disagree more!

We moved from a house 3 years ago with gravity fed tanks in loft to a house with unvented Megaflo and dry loft and we love it. Mains pressure showers and baths and no need for shower pumps.

Megaflo is not hot water on demand, that's what you get with a 'combi'. Megaflo will have a 'system' boiler. The Megaflo cylinder is just for storing hot water, not for C heating although the boiler will heat the water in the cylinder.

C heating is heated straight from the boiler with sealed 'under pressure' system no expansion tank in loft required it will have a metal (red) expansion vessel instead usually in the airing cupboard.

I didn't really know how they worked when we moved here but taught myself the basics of how it all works and it's fairly straightforward. You are not really supposed to do work yourself on an unvented cylinder and plumbers working on UV cylinders should be 'G3' registered. Yes there is more to go wrong than with a traditional gravity fed system but we have had no problems so far and in my view the benefits of this system outweigh the disadvantages with regard to maintenance.


EDIT: Heating and hot water can be controlled independently

MisterP123

They have considerable benefits over older gravity fed systems, or are you comparing them to a combi? Not sure what knight is on about with a "standard system."

The water in the tank does need to be hot, obviously. Personally, with modern tanks and boilers I'm of the belief that it's probably more economical to keep the hot water on constantly unless you are away for any period of time. They're well insulated and retain heat well.

To contradict the above, it's also possible to have hot water and central heating through a single tank. These are very simple systems on paper (no valves for instance) but if not set up and run correctly are horrendously inefficient. They're typically designed for people who have the ability to use more than one heat source (your boiler) to keep the water in the tank hot.

Browntoa

I've had a combination boiler at my old place, poor hot water pressure and temperature.

Moved and have system boiler with a megaflo tank , good pressure and constant temperature. Worse case scenario the megaflo has an immersion part to heat it.

Wouldn't go back to a combi

Typhoon2000

The unvented hot water tank is pretty much the ‘standard’ System now in new property big enough to house a hot water tank.

Water is stored under mains pressure in the tank and heated indirectly by the boiler. That means there are coils than inside the hotwater tank where hot water from the boiler pass through. The water in the tank can also be heated directly by an inbuild immersion heater should the boiler not be working.

As the tank is pressurised, it can sited anywhere in the house including say the grarage, it does not have to go in the loft. It holds much more water than an old fashioned vented tank ( mine is 300 litres). It is very efficient at holding heat- one hour of heating by the boiler is good for the whole day.
Unlike a combi you can have both heating and hot water at the same time, and have more than one hot water tap or shower on the go at one time. As the water in the tank is always hot, you do have instant hot water on demand ( unless you empty the tank without heating it again - which is hard to do if you have a decent sized tank). And the hot water out of all taps is sealed mains water and drinkable like the kitchen tap.

knightstyle

The trouble is that it has to be repaired by an unvented qualified person. Ended up costing her nearly £1000. Any problems on our tank in roof system are easy for me to fix and yes we have a pump I fitted to boost pressure for the showers.
See my thread about DDs problems https://forums.moneysavingexpert.com/discussion/5614427/help-with-central-heating

keith969

I think you've been unlucky, but do agree there's more to go wrong with them. In the last 10 years I've had to have the PRV replaced and a new expansion chamber, apart from that it's been very reliable.

ess0two

knightstyle wrote: »

The trouble is that it has to be repaired by an unvented qualified person. Ended up costing her nearly £1000. Any problems on our tank in roof system are easy for me to fix and yes we have a pump I fitted to boost pressure for the showers.
See my thread about DDs problems https://forums.moneysavingexpert.com/discussion/5614427/help-with-central-heating

Your comparing the fact that you can repair / fiddle with an unvented system,if you weren't that handy then,you need to pay a plumber regardless of the system fitted.

bris

£1000 to repair an unvented cylinder? please tell what could possibly cost £1000 to replace?


I have the unvented systems on my ticket, installed a fair few but have yet had to repair one, very little to go wrong with them.


Replaced plenty actuators but they only control where the water flows.


This is the right system for a 2 bath house.

fezster

Gravity fed systems have repair costs associated with them also. After all, with gravity you have a hot water tank, a cold water storage tank (full of water in the loft with the risks that come with that) and potentially have pumps to showers if you want a powerful shower experience, all of which can also go wrong.

An unvented tank, in comparison, has a few safety devices which require checking annually, but otherwise is mains fed cold water, so as long as your mains delivers good pressure and flow, you get good shower performance with no stored cold water and no pumps. Unvented tanks are also extremely thermally efficient, being internally insulated, and so will retain their heat far better than the old copper tanks with insulation attached to the outside.

I know which system I'd choose (and did).

My view of combis is that they are suited to smaller households only. They are also far more complex and potentially more expensive to repair if anything goes wrong. They have their uses though, where space is at a premium.