replacement boiler

I don't think my sons lady gardener would be happy to do that if he decided to do away with the outside toilet:-)

Mike

NO! I mean a boiler which just heats the water passing through it, without a built-in pump and expansion vessel - and *definitely* not a combi! Heat-only is the correct term. That doesn't mean that it can't run both the central heating *and* the domestic hot water with suitable external valves and controls - which the OP already has.

My mistake. I don't actually recall coming across any heat-only boilers when I replaced my last combi, but I was probably looking at systems.

That sounds like a term for the razor he uses to tidy up his partner's pubes.

It's not "modern rules" that cause the need for a larger gas pipe - the rules are the same as they have ever been - 1mBar of dynamic pressure drop allowed in the pipework between boiler and appliance.

IME there are three reasons that an upgrade is commonly required:

Here is the procedure for working out what size piping you actually need:

On the compost heap (men only, a woman's piss is no good.)

Vaillant does a combi with a storage tank built in. A friend who deosn't like combis is very interested, especially as her boiler is close to the sink. It'd be a lot slower to the bathroom though.

I thought a woman's was a bit more acidic, and more likely to contain hormones which might need care, but still a good source of nitrogen worth adding.

Should get good firm cucumbers et. with it! The difference is more in aiding decomposition AIUI. A GF told me 'men only' and she does research a horticultural organisation on a voluntary basis.

Ok so probably my old boiler was under piped. The manual for the new Worcester Bosch says the feed pipe must be 22mm.

I have no idea why the old boiler was on smaller pipe. It was a conventional flue unit, replaced with a balanced flue of similar heat output. It was only replaced because of issues with the chimney...

Dave

Just sharing my personal experience of a boiler swap last June. 10 years ago we had a loft conversion to our 4 bed detached - additional 3 rooms inc a bathroom. The system was converted to a sealed system to provide mains pressure hot water. The Potterton 12kW (output only 9kW) heat only boiler wasn't changed and soldiered on for a further 9 years but it was starting to get very noisy so we decided to take the plunge and replace it as it would only let go at the worst possible time when it did eventually fail. We decided to go for a heat only boiler as the other components (pump, expansion vessel) were in good shape and easily accessible for maintenance. We had 3 different boiler sizes quoted to us, 14, 18 and 21 kW. We decided to chose the installer who recommended the 21Kw (not the reason for selection) but for an extra £50 I upped it to 24Kw. We now have a W-B Greenstar 24Ri fitted. Runs on the 15mm gas supply (the meter is only a 4m straight pipe run away). The time taken to re-heat the cyclinder is considerably shorter (esp. when the heating is on) and the house gets to temp in short order (as you would expect). We did consider getting a fancy remote control boiler but why spend the extra money? I have subsequently fitted a nest thermostat so can do whatever is needed remotely. The new boiler is using approx. 30% less gas and is very quiet. 10 year gurantee with the mag filter installed.

Do the sums in the article above (easy for a single boiler). You can then find out if the problem is 2 or 3 from the list above!

For my new Vaillant, same output as the old one, both installer and man from Cadent wanted to know if the pipe was 22mm all the way - it is. From the table in the wiki, the run would have been about twice the needed capacty in 15mm but, as the boiler is very close to the (electric) cooker, it's worth having 22mm for the future (not me - I hardly use the ~15 yo Belling). The old boiler had 22mm into it; the new one is 15mm and it was easiest for the installer to put in the last ½m in 15mm.