Combi boilers

[Derek Geldard]

Be warned. It was "Brass Monkey" weather this morning. :-((

DG

[Styx]

We have had one for a little over two years -- it's in a 4-bed house, but only 2 of us live here. There's a fairly high-end thermostatic over-the-bath-type shower running directly from it, plus the CH and other DHW. It replaced a traditional boiler + DHW storage cylinder arrangement and a truly awful 7.5kW electric shower.

Before paying for anything, we read a pile of technical literature, talked to the Corgi chap, measured the incoming water flow rate and pressure at both the kitchen sink and the first floor bath (within tolerance, but towards the lower end of the scale), and even checked that we were going to be OK with respect to the length/capacity of the gas pipe feeding the boiler (long Victorian house, with the boiler being sited upstairs near the rear of the property).

To be fair, if you flush the loo or turn a tap on when the someone is in the shower, then the shower flow-rate drops a bit (more if you flush the loo AND turn a tap on, etc). However, we used to get that problem with the crappy electric shower we used to have, so that's not an issue for us. At least with the new shower the water coming out of the head is at a pretty damn constant temperature, regardless of the flow rate. When it's *only* the shower using water, then the pressure is way more than adequate, the wall mounted shower-head being easily able to spray the opposite wall (about 6' away).

The bath fills at roughly the same speed as it did pre-combi (I never timed it, so can't be precise, but it doesn't seem to take significantly longer), but the part we love is that we *know* we're not going to run out of hot water or can only take a bath when we know there's sufficient hot water in the tank.

It's only two years old, but the boiler has behaved flawlessly in that time. Our gas bills are a lot less, too, but then the previous boiler was about 25 years old, so that's no major surprise.

On the other hand, I have a friend who had a combi fitted about 3 years ago by BG. He considers it to be the worst POS he's ever had, plus nearly all his hot taps leaked (and a few rads) just after BG had fitted it. I asked him if they'd measured the water pressure/flow rate etc. prior to fitting, or advised him about the fact that the DHW & CH systems would now be somewhat pressurised, to which he said they hadn't told him anything and hadn't (as far as he knows) measured anything. Go figure.

Styx

[Doctor Drivel]

I meant one bathroom.

If you have a gable end consider a loft installation. You can also have the flue through the roof tiles too. More expense but worth it if it frees up space. Then the boiler can be mounted on metal unistrut tied to the rafters and joists. You will need a shoot down ladder, boarded from hatch to boiler, permanent light over boiler, a rail around hatch if near to boiler. They don't like the boiler being used to rest items on it for storage. So wall mounted high up prevents this, or on unistrut.

The condensate pipe can be run over to the 4" soil pipe if running through the loft, or down to the bathroom area or outside via the loft and into the soil pipe if outside. Insulate the condensate pipe to prevent freezing.

[Doctor Drivel]

Some combis have a small integral water vessel to prevent this.

[Doctor Drivel]

This man should eff off.

[Doctor Drivel]

Take not notice of this idiot. Combis have no limitations as there is a model out there that will give fast delivery and high flowrate delivery too.

[Doctor Drivel]

The Atmos is very simple. You tend to get what you pay for in combis.

[Doctor Drivel]

What models? How much did they cost? Were they installed correctly? The best tend to cost more - as with any appliance.

[Doctor Drivel]

Do not generalise. There are combis that can do 3 bathrooms. Many are just brilliant.

[Doctor Drivel]

Take no notice of this idiot.

[Doctor Drivel]

Which model do you refer? Many can fill baths faster than storage systems.

You should get to know more about combi boilers.

[John Rumm]

You get what you pay for to an extent. So go with decent brands and at the higher end of the power specs on the boiler and it will do what you want.

The procedure needs a little planning, but is not that difficult. When I did mine it went something like:

The present shower over the bath is a pumped system, can the pump be

Yup, you can't generally pump mains water, and the hot will be at mains pressure.

Which makes life simpler. If you are replacing the shower anyway you don't even need to worry about the shower feed particularly.

See Ed'd boiler choice FAQ, he spells out many of the details that tend to influence the reliability etc. Also remember to compare like with like - you can't buy a basic cast iron lump with minimal electronics any more so there is no point comparing a combi with that.

A modern condensing boiler designed to be one from the outset (rather than a old design that has been reworked to be a condenser later) will tend to be better.

Reasonable starting point with links to the other FAQs etc:

[Doctor Drivel]

You can't pump mains water, unless you have special permission.

[Bazza]

Have you got a link for this?

he spells out many of the details that tend

Thanks John for your input, as the new boiler will have to last for the next 20 years+? I will do a proper job and not go with the cheapest available. Useful information

[Doctor Drivel]

It is about 20 years out of date. Just ask me.

Good quality combis will last 20 years and more.

[John Rumm]

You have a unique way of adding value to a conversation dribble.

[John Rumm]

If you cold water main can supply water that fast...

[Doctor Drivel]

You got that right.

[The Natural Philosopher]

Mmm. That means every single electric shower is illegal.

[Ed Sirett]

Whilst our resident "quack" has abysmally low Signal:Noise in his posts, in this matter he is right, IMHO. Electric showers are quite legal and I'm at a loss to know why you think they aren't, the ones which connect to the mains (the majority) don't contain pumps.