Boilers

John, thanks for your suggesting about the PCBs but at 20 years old I think it's time to replace the whole thing and also it will be quicker.

One possible problem regarding rating and the way new boilers work - our gas supply pipe to the current boiler is 15mm - is this likely to be a problem for a condensing system boiler - I know it would be for a combi boiler. Maybe there is a ceiling on rating or some makers only specify 22mm.

Digging up the kitchen floor is not a great option...

we have a 75kW boiler with a 22mm supply. The boiler specification sheet should tell you the size of supply pipe needed.

At that age it owes you nothing, so probably worth going for a new system since it will cost lest to run as well.

(whether it will also last 20 years is another matter!)

A new 24kW boiler will have the same maximum gas rate (or possibly slightly lower[1]) than an old 24kW boiler. So in that sense - no it does not need upgrading if its already adequate.

(also worth noting that even very high consumption boilers often sitill have 15mm inlets - the anticipation that the end user will likely want the "show work" pipes in an out to be as unobtrusive as possible).

However to complication matters there are lots of "rule of thunb" fitters out there that don't actually do the sums and just insist that it needs a 22mm feed whether it does or not. Since that way they are covered, and very few end users would question it.

Do a quick set of sums to check the actual state of play:

You can convert between units like this:

It will tell you the size of the inlet, but can't realistically tell you exactly what you need unless it also knows the length of pipe, the configuration, and the demands of other gas using appliances.

(basically it would need to reproduce large swathes of BS 6891 "Installation of low pressure gas pipework of up to 35 mm (R1¼) in domestic premises (2nd family gas) ? Specification" to give an adequately complete answer[1]

(and 75kW is beyond the maximum output of a domestic U6 meter - so

Agree. My Viessmann is 12 years old now. Only had one major problem with it - when it was only a few years old the igniter unit failed and took the PCB with it :( A fixed-price repair from Viessmann direct, which included a service (the only service it's ever had!), and it's been fine ever since.

If I had to replace it now, it would definitely be with an Intergas.

when we bought this house it had no gas supply. It had once, but all pipes and the meter had been removed. The new supply and was fitted for a "Boiler exchange" scheme run by British gas.. I assume they knew what they were doing.

While Intergas seems to be worth considering I wasn't able to find clear evidence earlier this year that they were more reliable than other premium brands. My Dutch is non-existent but even Consumerboten seemed not to give them a clear lead over Vaillant for combis.

ROFLMAO!

It's something we hear regularly. Only time will tell.

My Viessmann has all the peripherals supplied via individual fuses on the PCB. I found that out with its only failure. A hose split, and water took out the gas supply valve. And the fuse on the PCB, which is a soldered in type. Cost pennies for me to replace that fuse. The average repair man would have fitted a new PCB at a cost of many hundreds.

They probably fitted a "bigger" meter - i.e. one more typically used in small commercial applications.

The normal U6 can do up to about 65kW or 6 m^3/hour. The next one up is a U16 which will do 173kW or getting on for 16m^3/hour.

What model boiler is it out of interest?

Do you have a diagnostic chart for the boiler (sometimes found inside the casing and/or in the installation manual)? There may also be some LEDs to indicate how far it has got in its startup sequence.

There is probably a pressure switch which operates when the fan is running fast enough to generate the required pressure. The pressure switch needs to operate before the igniter will attempt to work. So, if there's no signal from the pressure switch, it may be due to:

• fan not running fast enough
• pressure switch failure
• disconnected or broken rubber pressure hose(s) to name but a few.

If you do decide that it's new boiler time, both Worcester Bosch and Vaillant are pretty good. I had a new WB boiler fitted in my holiday flat a couple of years ago and have been very pleased with it. And I recently had a Vaillant boiler fitted in my main home, to replace the old Baxi. That seems pretty good, too - AND came with a 10-year warranty. One consideration for me was that space constraints meant that the boiler needed to have its flue coming straight of the back rather coming out of the top with an elbow to go out through the wall. WB flues all come out of the top, whereas many Vaillant boilers can have either top or rear flues.

expensive and not well known though ... asked 3 boiler engineers (BG and SSE),never worked on one, never seen one.

My neighbour has exactly this issue, boiler been running fine for several years, board failed ..... British Gas came out and checked gas pressure ... and now won't fix boiler unless he replaces 15mm supply pipe with 22mm T His remonstrations that they have serviced it every year and been happy are irrelevant. He has just replaced the 22m pipe, and they have now replaced boards and removed the 'do not use' sign. Surprisingly they were happy he had changed gas pipe and made new connections at meter & boiler.

The first may well be a statement of fact. The fact that they?ve never seen or worked on one could be down to their reliability! ;-). Either way, it doesn?t tell you much.

Tim

Fortunately that is not true of the WB oil boiler I had fitted a couple of years ago.

maybe you could find a similar used one & swap it, but probably you won't

In most cases a 24kW boiler is not permitted to run on 15mm now, current regs are more demanding re pressure drop. Worcester Bosch do a pdf: Technical Training Bulletin: Natural Gas (G20) Supply Pipe Sizing. that explains how to calculate what's required.

NT

Do you have a link?

We had a new Vaillant condensing system boiler installed yesterday and the installer played it safe and put in a 18kw unit as he said the 15mm gas pipe run was probably quite long and it is about 4 metres in a straight line from the meter without taking into account the true path under the hallway/kitchen.. The boiler so far is working fine and we have hot water and heating after 10 days without and it's comfortably driving 15 rads in about the same time as the old 24kw unit.

Only hitch was a bleed hole rounded off in one old rad so that's been taken out of the system for now.