new boiler advice

[Beelzebub666]

Hi all,
I have an old boiler which is beginning to break down a little too regularly, so I'm planning to have a new one fitted. The current boiler is wall mounted in the kitchen extension, vented straight out through the wall it's on, non-condensing. There's a hot water cylinder and pump in the airing cupboard, and a pressure vessel in the loft extension. Loads of space on the wall for a bigger boiler, any new one would go in the same place.

It's a 4 bedroom house with loft extension, and although it's just me at the moment I want anything installed to be suitable for the full sized family that will buy the place, as I'll die or sell within the lifetime of a new boiler.

Radiators, all over ten years old, the plumbing to them is 15mm copper throughout -

3 large, 1 small on ground floor
2 large, 2 small on second floor
2 small in loft extension

There are 2 Bathrooms, but the one in the loft extension has an electric shower and no bath, so not much hot needed up there except for handwashing. I'm sorry to say there is a bidet though. It wasn't my idea.

Incoming pressure is over 8 bar with 20mm blue pipe, all mains water is in 15mm copper after that.

Gas runs to the cooker and the boiler, on 15mm copper T'ed near the meter.

OK, questions -
Would the gas pipe need to be replaced all the way back to the meter in 22mm for the latest boilers?
Do I have to get a condensing one?
Could a combi boiler that heats the water as it's needed do a house this size and would you recommend it? Is it cheaper than hot water storage e.g. for filling a nightly bath?
Are all my radiators going to leak if the system is flushed for the first time in a decade as part of a replacement?
Where did I leave my glasses?

Basically i'm asking what is the best boiler for a house like this?

Thanks for your time.

edit:

Just thought of one more thing - the drain off for the CH is on the hallway rad, but all the ground floor CH pipework is below floor level, i.e. below the drain off. Does this prevent a problem for desludging? Would it have to be accessed at the lowest point? What's the usual practice when there's a fair amount of pipe below the drain off point?

 

[stem]

Would the gas pipe need to be replaced all the way back to the meter in 22mm for the latest boilers?

This would have to be calculated specifically for your installation by a gas engineer. I would say likely for a combi, not so likely for a heat only boiler.

Do I have to get a condensing one?

Yes this is a legislative requirement, in all but exceptional circumstances

Could a combi boiler that heats the water as it's needed do a house this size and would you recommend it? Is it cheaper than hot water storage e.g. for filling a nightly bath?

Combis do provide mains pressure hot water and you loose the hot water cylinder (although some see this as a disadvantage) but they aren't for everyone. They are more complicated, as they have more internal components, they can be slow to provide hot water when the boiler is starting from cold, you are also reliant on the cold main supply being sufficient for all simultaneous requirements, hot and cold. Once a hot water cylinder is heated up, if it is well insulated it will retain the heat until required, but if you use only a small amount of water each day say just to wash some pots, or one load of washing, then a combi would probably be more economical. However, I've noticed that in warmer weather, the temperature of water stored in my feed tank in a warm loft warms slightly, so will require a little less heat from the boiler. The cold main feeding a combi will still be very cold.

Are all my radiators going to leak if the system is flushed for the first time in a decade as part of a replacement?

Probably not, but can't be guaranteed, depends on the condition of the system.

Where did I leave my glasses?

On the table in the hallway under the newspaper

desludging won't be a problem if you install corrosion inhibitor, and the location of the drain off you describe is normal, I've seen 100's like this, including my own.