Boilers

When shopping for my Vaillant boiler and unvented cylinder and some replacement rads, I approached our local plumbers merchant to get a price. They were pretty close to the best online price I could find for the boiler and cylinder anyway. So ordered it from them along with all the other materials I would need, and let them deliver and unload it straight into my garage. :-)

Yeah its surprising with modern ebus style controls that more makers don't offer that option.

So if you work within the 1mBar pressure drop permitted, your maximum pipe length will be somewhere > 3 and < 6m [2]

So if you take the 6m discharge rate, and scale it for the slightly higher actual demand you get :

actual length = 5.2m

So yup with 4m of straight pipe, potentially another 1m or so of equivalent length in elbows etc, plus the rises to the boiler and the meter, you would be pushing it at 24kW

(in reality it would probably still work since most boilers will be a little more flexible than the pipe sizing regulations would imply)

To me, it would make sense to be able to set things via decent software. Rather than multi-function buttons and the tiny screen menu on the built in programmer.

Of course the cry would then go up - what about those who don't have a computer or smart phone? I'd say good luck to a technophobe programming one anyway.

Yep second that:)....

And in the meantime they are claiming bounce back loans to buy property with !!.

Gulp. How big is your house ?. Surely anything over 38kW would put you close to the limit of a domestic meter anyway and usually need a 28mm supply.

It is, of course, me muddling imperial & metric measurements. in metric

Yup certainly. On the Vaillant VR470 there is a reasonable interface (large backlit screen) and jog wheel to select options etc - so not as bad as using the small LCD on the boiler, but it would still be better sat on a computer with a PDF of the manual open on the screen beside you.

Well the setup is usually the domain of the professional (present company excepted), so it seems perfectly reasonable for their business to own a laptop as well as a flue gas analyser and any other special kit required for the business of installing heating systems.

Ah, that seems more reasonable, and easily in the scope of what you can get out of a "normal" U6 domestic meter.

(although that would be 91k BTU/hour rather than 75k)

I didn't think so.

I think this is far more helpful:

I did find this:

(my previous calc was assuming that the input rate is 24kW, which is likely an underestimate, since most boiler specs now quote output power rather than input).

Oh, and I missed the brackets round the 6 x 1.9

If I redo my sum with their flow rate, that brings the maximum down to ~4.4m total effective length. (although they also indicate that the pressure at the boiler inlet only need be 18mBar rather than the 20 one designs for)

I have a vague memory that the calorific value (CV) for natural gas is permitted to vary over quite a wide range. I have absolutely no idea what value boiler makers [have to] use when quoting gas rates and power but do just wonder if the 24 kW is based on a low (if not the minimum) CV.

Your google must be better than mine. I did look for a short while but gave up.

I find it annoying when someone makes a claim and then doesn't back it up, the request for a link was genuine.

A stove was fitted where I've worked on a branch going to a boiler. It's a long length of pipe to both boiler and stove and I can can hear the gas ring change note momentarily as the boiler fires up.

That's a little worrying?

I think boilers are designed to cater for low pressures because of poor regulation rather than any assumptions about pressure drop in pipes.

That was somewhat tricky to find and then disentangle from the google redirect to it, since could not find an actual landing page that links to it. However it just dawned on me that I can now do a link search on that one. So we get to:

Well par for the course...

If it dips and then recovers, it could just be a reflection of the main gas governor taking a moment to adjust in response to a large step change in demand. (which arguable a long pipe run might actually smooth slightly, rather than make worse)

Well they say that's peak rate 10 mins after ignition. If the boiler attempts to modulate on actual output power rather than gas rate[1], then when the system is warming up, but not yet enough to modulate the output down, condensation efficiency would likely be tailing off a bit.

Quite possibly - but it also explains why a number of installations seem to work in practice, even when they their supply pipework is well out of spec.

So our new Vaillant has conked out tonight after working perfectly for a week. Won't fire up, just like the old Vaillant now scrapped, which also failed on a Friday evening.

It seems to be a gas valve issue and I hope it is and not intolerance with the supply. The only other gas appliance we have - a 5 ring gas hob - is working OK.

So all I can do is call out Vaillant under their warranty as the installer can't touch it without voiding the warranty.

This is distressing for the family...

I presume you?ve checked the system pressure (assuming it?s a sealed system)?

Tim

Pressure is about midway between upper and lower on the display.

The installer measured the appliance gas pressure at 20mbar so it should be OK. I called him and he said it may be a faulty gas valve. Not good for a new boiler and a brand rated as the most reliable.

Any fault codes?

Just because they are reliable as a group, it does not mean yours is going to be perfect!

Indeed. Vaillant engineer fixed it on Wednesday in 15 minutes - it was a faulty gas valve. But he let something slip - that the valves often fail and he said he'd fitted an uprated component. This tells me that there is stock being fitted by installers with a known issue, or at least known internally to Vaillant.

Anyway it has a 7 year warranty so they can keep on coming to fix it for free and I will ask for comensation for downtime.