What's the current combi boiler of choice?

[YAPH]

Ooo-er, I've been fitting a lot of those.

Why did you need to service one 3 years ago? They'd only just come out then.

[Tim S]

Dave Plowman (News) coughed up some electrons that declared:

Hi Dave,

I'm not committed on paper yet. So, in the spirit of open-mindedness:

Question: I thought one couldn't work DIY on hot pressurised plumbing - and that it needed to be checked every year? Did I get that wrong (that would be a deciding factor for me)?

The other thing is that, DPS do do heatbanks for sealed systems, but effectively you end up with lots of heat exchangers (assuming you run the rads pressurised too) so it seemed to make things more complicated with at least two different circuits to fill plus the cylinder itself which can't be pressurised (IIRC they do one with a little integral header tank and float valve, so we'll assume that should sort itself out).

Not sure how much it bungs the cost up to add these features - my spec is coming in at 1700-odd quid which is already too expensive, but I like the overall benefits of no CW tank (waste of space in my house due to attic conversion), mains pressure drinkable HW and I can get the solar coil option for future expansion as it costs very little extra on the tank.

Not to mention electrical backup for when the boiler dies (they always do, always at the worst time!). I'm getting 3 x 3kW immersion heaters in mine, which don't cost a lot, provided you stay away from their fancy built in controller (mine will have a contactor driven off a very simple timeswitch which will suffice in an emergency)

Always the way... I tried to solder a PCB with slivers cut off a stick of plumber's metal when I was a lad, for similar reasons. That didn't work very well (oddly enough!).

Cheers

Tim

[YAPH]

Yes, you got that wrong. Unvented (sealed) *hot water* systems are controlled by building regulations.

The DPS unit is just a box (some are even box-shaped). Hes it's got 2 heat exchangers in it (one a coil in the cylinder/box-shaped-store, one plate heat exchanger) but it Just Works. (Except when it doesn't of course :-))

I wouldn't bother with a solar coil option[1], any more than I'd consider a windmill except as decoration (our latest megaTescos has got an array of them on the roof of its petrol station: they look almost as good as the one on Teletubbies :-))

Yebbut when the boiler goes down you'll also be running a stack of electric space heaters around the place so demanding an extra 9kW for DHW may not be the cleverest move.

[1] apart from the appalling economics and ecologics of solar DHW in these climes, if you did still have money to burn in putting one in you could at least do it properly with a decent-sized store of its own rather than sharing a tiddly bit of space at the bottom of a regular store.

[Tim S]

YAPH coughed up some electrons that declared:

OK - Thanks... I assumed it was solely to do with having a pressurised system (and the possibility of things going bang).

The one I was looking at has no coils and one plate exchanger. It's so simple, you could pretty much make one from a very very big normal copper cylinder. If I could figure a way to add extra bosses, heater flanges and insulation to a simple copper cylinder I would. But it's not easy to do it properly (especially the insulation). Not forgetting of course that the DPS price includes all the pumps, mixer valves and heaters and stats.

Well, the coil is cheap as the unit is already there. I think it's a bit unfair to compare windmills to solar panels. Looking at it, I don't think the panels are worth it yet on payback grounds - but with the new vacuum tubes becoming cheaper and better over time, and gas becoming more expensive, I can see a time, possibly in the next few years that it might be a genuinely good idea.

The idea is just run a couple of rads off the system (as far as 9kW goes), but they can be any couple of rads as the day progresses. It's one of those things that's going to be a rare occurrance, but the cost of doing this is next to nothing. I'll have a couple of fireplaces open anyway, so two areas will be heated by wood.

That's a fair point. I've just thought it through... Here's what I think:

In summer, we don't use the rads (ha!) so we attempt to supply HW from solar, so we restrict the operation of the boiler and avoid daytime burns. We run the boiler overnight just to bring the system up to capacity.

In other times, solar may contribute, but we clearly need boiler input because either solar input is low or demand is high. This is the hardest case.

Now, I don't have room for an extra cylinder just for solar. The answer might be to give more of the cylinder over to solar, which would mean different takeoff points on the tank for the primary circuit.

It's an interesting idea. DPS are quite flexible and local to me (well, Epsom isn't that far from Kent). Might be interesting to consider having them put in an extra primary connection higher up (no coils, so it's just bosses).

Would allow for some flexibility. I can see how it might possibly be an advantage to alter the dynamics of the unit if we ever did have decent solar input. I'll have to think it through some more.

If there was a provable scenario where altering the flow dynamics were a good idea, one could add a 3 way valve and a computer later.

I think solar is "watch this space" but I am quite optimistic it will become a sensible option in 5, maybe 10 years. I'm not known round here for being a greenie-fad monster(!)

Cheers

Tim

[Tim S]

Tim S coughed up some electrons that declared:

I should have said "no coils on the boiler side".

[Dave Plowman (News)]

That only applies to the secondary hot water circuit - not the primary. But I'm not sure if it applies to every make of pressurised water heating circuit.

No idea, I'm afraid.

That's separate from a pressurized primary. I've kept my header tank for the hot water system - for all the obvious reasons. The space it occupies wouldn't be much use for anything else.

I've not investigated it, but it just didn't flow round the back of an awkward joint as I'd expect with leaded. The part you could see was fine. And I've done probably hundreds of similar leaded end feed joints without probs.

But I won't use lead free for electronics either. Too many reports of problems.

[Tim S]

Dave Plowman (News) coughed up some electrons that declared:

The company I currently work for still use leaded as they do vehicle electronics and that's exempted from the ROHS rules on solder as is medical and avionics. Says a lot doesn't it!

I really fail to see the point in banning leaded solder for potable fittings as the surface area of solder exposed to the water is bugger all.

I need to practise with some lead free joints. But if they are as difficult as this to get reliable, I know what I'll be doing.

Cheers

Tim

[Andrew Gabriel]

I've done quite a lot of lead-free, but the vast majority leaded. I can't really claim I notice much difference, except the lead-free seems more fluid, and sets with a brighter mirror finish.

Most of my component stocks are leaded, and likely will be for ever. I solder components at 800F anyway, and always have done even with leaded. It enables a quick soldering and exit.

[Dave Plowman (News)]

That's exactly the reverse of what I found. Although there could of course have been another reason. The joints that weren't made properly were ones where it wasn't possible to access all round, and although the solder flowed easily at the top and sides it didn't get to underneath. The pipe and fittings were new and spotless. I was using an active flux - the same stuff I was using for leaded.

Crikey. That is hot. I use about 350C.

[YAPH]

I thought you were looking at their Pandora units, but I think you're talking about their GX(?) models?

BTDTGTTS - see DIY heat bank in wiki.diyfaq.org.uk

They both have their places, but they tend not to be urban houses with mains gas and electricity supplies.

Ah, OK you're running the CH off the heat bank too - didn't realise that.

What about additives? Solar systems generally need antifreeze which means you'd hav eto dose your entire primary (boiler, rads and heat bank) with it too.

They seem to have been just 5-years around the corner for the last 2 or 3 decades. Heat pumps look to be a more realistic prospect. Google for McKay's "renewables without the hot air" or something like that for some clear thinking on the subject.

[YAPH]

I generally use solder-ring fittings which (I assume) have lead free solder, and have no problems. Possibly it flows less well or something: I tend to wiggle the joint once it's started flowing until I can clearly see a ring of solder to make sure it's wetted all the way around. Maybe it wasn't like that on the old leaded joints but it's so long since I used them I couldn't be sure.

There are brands of flux described as 'lead-free'. Since flux obviously doesn't ever contain lead I assume they're designed to work better with lead-free solders. I'm currently using La-Co, before that I used the Fernox stuff. It all seems OK though.

[Dave Plowman (News)]

That's what I wondered after my failures. But looking at fluxes in the PM non seemed to mention suitability or not for either.

[Andrew Gabriel]

700F (370C) are the more common bits for my iron, at least in the days of leaded solder, although 800F was always available as an option. It may be 800F is the default now lead free is more common. 800F bits don't last as long (the iron plating fails faster).

[Doctor Drivel]

Look at Broag:

[Doctor Drivel]

He doesn't understand so don't make an issue with him. Try the open vented Broag 18v.

[Doctor Drivel]

No. ATAG, Atmos, Broag, MAN are all better boilers. The Viessman 100 range is crap (made for the UK market) The 200 and 300 are better.

[Doctor Drivel]

Sealed (pressurised) thermal stores do not come under G3 and can be DIYed. The cylinder has no complex pressure controls. Effectively it is just a large pipe in the sealed CH system. Best have a 3 to 3.5 bar pressure relief valve on the boiler and cylinder. Backup if one goes. They tend to have that anyway.

look at:

[1] apart from the appalling economics

DIYing it makes economic sense.

[Dave Plowman (News)]

[Doctor Drivel]

Eff off you are an idiotic Jocko plant.

[Dave Plowman (News)]

Wot - no pot? Are you smoking it instead of your usual alcohol?