Boiler advice - combi or "normal" for a large-ish house?

[Housemum]

I'm hoping Pigletjohn or someone else with plumbing expertise might be on here!

Whilst this is probably the worst time to look at spending more money, I am seriously considering replacing our boiler. Reasons to replace:

• it's over 15 years old, we have to call the engineer out about once a year
• it's G rated for efficiency (realistically how much does it save moving from G to A? Last year we used about 19000 kWh?)
• not all parts are available any more
• we are paying £27 per month for the only service contract I could get to cover it (our home insurance includes "free" boiler cover but only for boilers under 10 years)

Our house:

• 4/5 bed detached (the 5th is a spare room loft conversion which just has a couple of electric portable heaters), 16 years old modern house
• wall mounted Ideal Classic boiler in the garage
• cylinder in DD3's bedroom (in what should be her built in wardrobe), expansion tank in loft room
• radiators (no TRVs) in all rooms except conservatory which has an aircon unit for heating/cooling

I love the idea of a combi boiler giving DD3 a wardrobe by losing the cylinder, but would the reduced water flow when using more than 1 appliance seriously piss me off? Quite often I have the dishwasher and washing machine going at the same time, and might then be doing some washing up or running a bath for the kids. I suppose I would need to be v organised about how I use water? How have other people found combis compared to "normal"? Our water comes out of the kitchen tap at 8 litres per minute.

What else should I be thinking of? (Other than how on earth I am going to afford it!)

8 litres per minute is not enough.

Without a tank, that would take about 12 minutes to fill a bath, provided no-one in the house was running any other tap of flushing a WC.

20 litres per minute is about the least you need, which can fill a bath in 5 minutes.

But possibly you have a fashionable new Italian mixer tap that strangles the flow.

How old is your house; is the ground floor wood or concrete; how far is it from the internal rising main and stopcock, to that point in the pavement where the front gate used to be, or where the water meter is?

Do you know if the incoming service pipe is lead, steel, copper of plastic? You may need to have a trench dug and new water pipe laid.

You can run a modern cylinder off a modern boiler and it can be very efficient.

BTW when I changed my 25-year-old iron Potterton boiler for an efficient modern one, the gas usage dropped by about a third. This is far more than I would have expected, but I would have thought 20% should be a reasonable expectation. I still have a cylinder because I prefer it.

Thank you for the advice :)

We have got a single flow mixer tap (sore point, that one, but nowt I can do about it now!) But just checked bathroom tap and still only 9 litres in a minute.

House built in 1996, ground floor concrete, the stopcock is near the back of the house (corridor, kitchen with stopcock, conservatory/dining room along the back), the water meter at the front so I guess 21 metres?

No idea on pipework - something cheap in 1996 judging by the way these houses were built!

Well, it looks like it will have to be a modern "ordinary" boiler - and forget having the wardrobe! (Unless I want to spend hundreds on moving a cylinder - the reason for the odd position is that when the loft conversion was done the staircase went up through the old airing cupboard and the cylinder was moved into the upstairs box room/study/minute room pretending to be a 4th bedroom)

If the house was built on 1996, there is a good chance the incoming service pipe is blue (or black) polythene. At the stopcock it might be reduced to 15mm copper. The plastic pipe wil probably be 20mm or 25mm - it may be printed on the side of the pipe, or cast into the brass stopcock, or you can measure it. It may be possible to improve the flow. See if you can measure or read the size.