One unvented tank or two combi boilers?..

[Arjay12345]

Hi

I have recently installed an invented Ariston tank and Valiant system boiler, and have been running for 9 months. I'm now not sure I made the right decision and instead I should have installed two combi boilers - one for each floor of the house.

I find heating the tank tricky as I have now put the boiler on a timer to heat up the tank at three times thought the 24 hours as I it became apparent its a waste to keep the boiler running 24 hours a day. But then I can be left without hot water at weekends if we have guests over and extra water is used than the 300 litres, and I forget to extend the boiler timer. With a combi, the water would literally be on-tap.

And I had a new 25mm supply pipe installed so supply should not be a problem. Pressure was tested by water company, and far exceeded the minimum.

What have others done? Or have I just missed the point of an invented tank?

Thanks..

 

[gas112]

Get a timer where you can set weekends different and leave the water on once ie all day .
Unvented beats 2 combis hands down .
You have to remember also if using lots of hot water on a combi in winter the heating will be off for extended periods of time .

 

[mysteryman]

It would indeed be 'a waste to leave the boiler running', but in fact it should be thermostatically controlled and will only heat the cylinder when it cools down. This will not be often, because the cylinder is well insulated.

 

[Agile]

Fitting a boiler when you are not Gas Safe or certified to install unventede cylinders?

 

[Whitespirit66]

Ripping out your new system and installing 2 new combis, plus all associated pipework, etc. etc, etc and the increased cost of repairing combis when they go wrong (less reliable than a system boiler and you will have 2 of them) is going to take quite a while to get back in any gas costs saved.

As said, a 7 day timer is the way to go.

 

[dcawkwell]

It sounds as if your water requirements exceed the tank capacity a little.
I have the same setup as you. The boiler comes on and heats the water
for 1 hour in the morning and 1 hour late afternoon. That provides us
with all the hot water we need. Granted if you have two people run a bath
after the boiler has heated the water then all the hot water is gone until
you fire the boiler but that is just the way the system work.
A reheat of the tank takes all of 30 minutes from cold so it is there
at the flick of a switch.
A cross between a combi and hot water tank like the glow worm ultra power which defaults back to combi should the tank run out of hot water might have
been a better choice.

 

[ianmcd]

Sorry but although you have received some genuine replies you have also received some false information if you have a modern unvented cylinder the heat recovery of these units are exceptionall, and you should leave your boiler thermostat at maximum and leave your hot water timer at 24 hours, modern units do not lose much energy and will only replenish any hot water you have used

 

[Arjay12345]

All

Thanks for replies. Family emergency meant I couldn't write back earlier.

So I get the point around heating being off in winter. And definitely not looking to rip what I have out and start again; it's merely a hindsight question.

I already have a timer which works fine for us, and the tank capacity is fine. The problem is only on those rare ocassions when extra bathing water is used and I haven't extended the timer on the boiler.

I guess my grey area is tank reheat time from cold. My Ariston has 'TBC' in the tech spec. Plus the heat loss over a period of time. If I had both those facts, I could tweak things for maximum efficiency. Does anyone have these, even for another tank brand (300 litres). I know 30 mins reheat has been mentioned but is that what the spec says?

I have a load of home automation installed too so can further automate too.

Thanks

 

[ALEC1]

your best bet is too use the vaillant controls centre...vr65..that way you cannot have a mismatch of the thermostats and you get hot water priority automatically...

ariston is a good cylinder with decent sized coils so recovery will be very quick...but you do need how water priority...

 

[mysteryman]

You are worrying about a problem that does not really exist. You could leave your hot water enabled 24/7 without significant losses. The boiler will only reheat the cylinder when either you use hot water or the cylinder cools due to heat losses. As the cyl is well insulated, this is very infrequently. Otherwise, just time it for when you may want water; when you are at home.

 

[AlexCarp]

I was surfing and found this old thread. Interesting. Having been impressed by the simple and highly reliable Intergas combis. I did some ballpark figure for a new two heating zone, two bathroom installation. The Intergas can deliver approx. 14 litres a minute, so two can deliver 28 litres per minute. That is a substantial 840 litres of hot water delivered in 30 minutes. Two Intergas combis can be fed from one U6 meter.

Looking around a 500 litre quality stainless steel unvented cylinder is going for over £1,100. A quality Intergas boiler for around £800. That is approx. £1,900. Then the three expensive zone vales, wiring, etc. So over £2,000 for quality kit. Recall the cylinder can only deliver 500 litres, while the two combis can deliver far more at 860 in 30 minutes. If a larger cylinder is needed to match the two combis hot water delivery then the price is even higher.

Two Intergas combis can be had for £1,700 and no zone valves or other complexity is needed. They take up far less space than a boiler and very large cylinder. There is far less complexity and quicker to install. The Intergas combis have only 4 moving parts, hence highly reliable and are built like tanks.

Each Intergas can supply a bathroom each. If a bath needs filling quickly then the DHW outlets can be joined only for the baths using check valves. As as the OP mentioned each combi heats a floor each and the Intergas combis have weather compensation as standard.

I agree with him that he should have gone the two combi route in expense and clearly convenience, as he is heating up the cylinder at various times of the day. A combi has no such issues.

This is a case of the installer not assessing the options on market.

 

[simond]

Which model Intergas?

 

[AlexCarp]

Which model Intergas?

There are three take your pick. The specs are on their web site.

 

[Dan Robinson]

Jesus.

 

[AlexCarp]

Jesus.

The specs are on the Intergas web site. Look.