help with boiler decision

[geoff]

In message , geoff writes

Oops not there, I'd better rectify that, meanwhile, apart from the part number - see here

[Derek]

I'd add that you shouldn't take at face value manufacturers claims about combis supplying "N" bathrooms. We have a 35 Kw Bosch greenstar and it can't supply the hot taps on 2 handwash basins (1 upstairs, 1 down) at the same time.

They are more complicated nowadays

I suspect it's basically a training issue viz the service engineers. It's hard to get service engineers to put their heart into learning about old kit that only exists in declining numbers. BICBW.

If you can get the old one out. Bear in mind the cylinder has little strength when empty ( Don't forget to empty it will you :-) ), one of mine was little more than a copper balloon.

OTOH The thermostats are usually cheap and easy to replace.

[<me9]

If getting a combi (with a pre-existing cylinder) it can be used to give mains pressure showering, and the tank for stored water for everything else.

[Dave Plowman (News)]

Au contraire, my little mentally challenged one. I bought the mixer I wanted in the full knowledge it might require a pump. Some of us here do have some practical experience of problems and how to solve them. So get back to your catalogues and dreaming.

[Dave Plowman (News)]

Which are well over 100% efficient, of course. Most people here will know by now to take your definition of high flow with a pinch of salt.

You're certainly a pro. What in is the question. Certainly not anything to do with the design or installation of heating systems.

Yeh - everyone is wrong but you...

[Dave Plowman (News)]

Seems to me to give the worst of both worlds in some ways - you have the reliability issue of a combi and the space usage of a storage system. I suppose if you have baths every day the efficiency of a well insulated cylinder should be ok even when not supplying other areas. I'm not quite sure why you'd be concerned about having potable hot water in the kitchen? For making tea etc the important thing is fresh water - and you'd usually have to run off quite a bit to get both that and hot from a combi. For other uses does it make any difference?

[Dave Plowman (News)]

That's interesting - what do you consider to be a high maintenance cost risk? And is a low pressure system more at risk of leaks than a higher pressure one?

Of course with a storage system you can have a backup in the form of an immersion quite cheaply - just make sure you buy a good quality SS one so it works when you need it. ;-)

[Derek]

A 50 gallon tank replenished automatically by a float valve in the loft for a start. If it leaks when it's full what can you do?

We had one where a plastic bit popped off the float valve and whenever anybody drew hot water it sprayed the interior of the loft with water, of course some of it landed in the tank so it shut off eventually and no fault was apparent for many weeks by which time there was a ceiling and a built in wardrobe to replace along with a lot of clothes.

Maybe less, but the consequences of a failure involving that 50 gallon tank are I feel more serious. There was a very sad case quite recently of a badly installed tank being softened by continued pumping over and discharging it's contents which brought the ceiling down killing a child in the room beneath by scalding.

Bet they're still made in China. See my post about cheap rubbish Ty-wraps. 8-(

Derek

[Ian & Hilda Dedic]

thanks for that info, I'm hopeful the worcester bosch chap will be able to fix it now.

thanks for you comments guys, I'm interested in the combi + yank idea if we have to go that route eventually

dedics

[Doctor Drivel]

Please eff off as you are a total plantpot.

[Doctor Drivel]

Please eff off as you are total plantpot.

On the news they said that over 100 people escaped from psychiatric units overt the past year.

[Doctor Drivel]

That gives around 14 litres per min.That will supply two basins OK. Sounds like something is wrong.

Which means nothing. A quality boiler well fitted in a clean system will last 20 to 25 years.

[Rod]

I am not that concerned about potable HW - but there certainly can be times when cooking a meal that it would be convenient to have a head start over cold water. (Usually when I have forgotten something...:-) )

Another factor is the long pipe from the HW cylinder to the kitchen tap

- whereas it is common to have a wall mounted boiler in the kitchen quite close to point of use. So less heat loss from pipes as the HW does its round trip to upstairs/across the house and back.

The cylinder would really be used for baths and showers - as it already exists and can provide a good flow rate. So maybe possible to use a next-size-down combi? (It is possible that this would have a cascade of savings - no need to upgrade the gas supply to support a Drivel-o-matic super-combi at 54 KW, not so worried about having high mains flow rate, etc.)

Haven't looked today, but a while ago it seemed to me that the difference in cost between a combi and the equivalent system boiler sometimes was remarkably small.

[Doctor Drivel]

In-line instant electci water heater can be in a combi outlet for backup. Plantpots don't know this.

[Doctor Drivel]

Good point.

[Doctor Drivel]

Take no notice of this plantpot. Quality combis are very reliable. Buy an Atmos - they just do not go wrong.

[Doctor Drivel]

May as well get a high flow combi and do away with the leak prone tanks and cylinders.

[Doctor Drivel]

Do not have a combi and tank/cylinder. Just get a quality high flow combi and get rid of the rest.

[Derek]

Just measured it. 7 seconds to deliver 1 litre. Delivery slows to a trickle upstairs when a downstairs tap is open. Roughly speaking starting with the water running hot it would take a full minute to fill 2 basins with a gallon each, except downstairs is getting the lion's share.

Oh, and another thing, despite having the pre-heat on (that comes and goes and the water just goes cold again) it takes a good minute to get to the point of delivering hot water.

Except the maintenance cost ...

The ironmongery maybe, I'll take your word for it. Myself I reckon it will be leaky and corroded by then.

How many sets of motorised valves and gas controls not to mention PCB's will it have eaten in that time ?

25 years is a *very* long time for electrolytic capacitors and components which run hot such as rectifiers, or have moving parts like relays.

Derek

[Mark]

Good luck! FWIW I think one of the reasons why combis are so popular nowadays is they are easier to fit (where no system already fitted) and so the plumber can make a bigger profit. Afterall there's no cylinder, external pump or header tanks and associated pipework.

When we replaced our boiler we went for a storage combi (washing machine size) due to price and the fact that we had no convenient place to put a cylinder.

We can fill a large bath quickly and it even coped with two baths filling at once. When the heat bank runs out the water goes colder, but this does not happen very often.