PigletJohn has made more than 500 posts with the word boiler in them, but i'd still appreciate help with making a decison (from anyone not just PJ!)

[PuraVida]

we are finally going to replace our ancient back boiler - hurrah!

i need to decide whether to get a combi or conventional boiler and i'm flummoxed

we have a three bed semi plus a loft room. currently only one bathroom and it would be brilliant to regain the space taken up by the hot water cylinder in the smallest bedroom and the cold water tank in the loft.

it would seem that a combi would be the better option based on this, however we hope to extend eventually. This certainly won’t be for at least two years, possibly more, but it is an eventual hope and would include an additional bathroom.

I have researched lists and lists of pros and cons of each type of system, but I just can’t make a decision

Is there anything to be added that could swing me in either direction?

two people using water at the same time? Get an unvented cylinder.

Start by measuring flow (litres per minute) at your kitchen cold tap. Look at your incoming water supply pipe. Is it iron, lead or copper? How old? What diameter?

We went with an unvented system and had a new mains pipe laid as per PJ suggestion.

Fabulous hot showers on all 3 floors and really cheap to run.

At present no, there's only one bath and we never wash up so only one using at a time

Is an unvented system something different to a combi or conventional, a 3td type? Does it need the big, existing cylinder.

Is the incoming water supply under the sink? I imagine it's old. It's a 1920s ex council house and hasn't any dignificabt modernization

Ok so an unvented system is a megaflo type thing. Don't say I have t read at least done of your 500 posts!

Wouldn't that be overkill for a one bathroomed house? The extension is something of a pipe dream at the moment. Is it worth putting one in even if we don't extend for 2-5 years?

Christ sorry. Using phone in bright sunlight and cannot see typos

An unvented cylinder would be new, usually larger, and runs at mains pressure. It is fed off the supply and there is no cold tank required. It is better insulated and heats up faster. Properly plumbed, it gives unsurpassed flow and pressure.

If you have a combi, and poor flow, your showers will fluctuate if someone flushes a WC, or the washer or dwr starts or stops taking on water.

A 1920's house is probably ready for a new supply pipe, in a larger size.

Unvented you have a large storage cylinder and a small one - it can be elsewhere near by or above it depending on space. We don't have a cold water storage header tank though.

I think if you plan to extend it could be a false economy not to have something more suitable than a combi.

In our previous home we had a combi and it was fine as it was a very small 3 bed - you knew if someone was in the shower etc. we also had a shower fitted with erm a special temperature thing so when the pressure dropped the temp stayed ok. I wouldn't have one in a home where you couldn't easily tell who was doing what. There again I am someone who needs a decent shower just one of my things and wouldn't want an electric power set up.

We don't currently have a shower

the small "cylinder" might be the white pressure vessel for the tap water. Boilers usually have a red one (=not for drinking water) to even out the pressure in the radiators, but it is usually hidden inside the boiler case.

Do the bucket test on your bath tap. Combis are noticeably slow to run a hot bath, especially in winter, unless you have a particularly large or special one.

On the rare occasions when a system or conventional boiler breaks down, you can continue having hot water from your cylinder using the backup electric heater. When a combi breaks down you have none.

Some gasmen object to me saying that combis break down more often.

believe me it's not through choice

one last Q before i can do the flow rate test when i get home from work.

would the cylinder for an unvented system need to be upstairs? we have a good large cupboard downstairs where the new boiler will go, could it be in there too?

Ours it downstairs, not where the original one was! Nearer to the new boiler the better I was told.