New boiler. Help stuck

[bm1981]

Hi all,

Looking for some good advice on boilers.

I've recently moved into a 4 bed semi with a bathroom and shower room. 14 rads. When we purchased the survey flagged the loft tanks as needing work. Anyway, the current boiler (potterton prima f) is very unreliable and about 20odd years old so I'm looking at replacing. I'm also having boiler relocated about 5 feet from shower room and into garage.

Direct change to another regular boiler (wb24i) is coming in at £2300 fitted. Not keen on this idea as the tanks are also in need of updating plus currently runs a whole house pump which is very noisy.

Option 2 is a wb38cdi combi. This is coming in at £3200 fitted.

Option 3 is unvented megaflow cylinder with wb24i system boiler. Coming in at £4500 all fitted.

My current flow is 17lpm then with two taps open 12lpm. Don't know pressure.

I've had two opinions from plumbers. 1st is that our flow is ok for combi and it will handle all our needs. 2nd guy said we should update mains from current 1/2" to 25mm poly to increase flow. I spoke to Thames water and they instantly told me on phone that 25mm would give me .83l per second 1bar. I understand that boiler input however is 15mm, so does that mean that the flow would be restricted back to current flow rate when the pipe downsizes for the boiler fitment or does some magic happen here??

What's the opinion on current flow rate adequate/inadequate for combi/unvented?

 

[doitall]

Hi 17ltrs/min is good for most combis, the more important consideration is, a combi suitable for the property, I don't think so.

With the mains upgrade the flow/pressure should be ok for an unvented, and of course it could go in the garage near the boiler, so would give you even more space in the property.

Ps, I would take 49ltrs/min at 1 bar with a pinch of salt, 30 ish would be closer, but still ok.

 

[bm1981]

Thanks for your reply. So the current 17lpm is no good for unvented, I'd need to upgrade mains? This will obviously increase the cost of unvented to well over 5k - fair quote for new install?

 

[doitall]

17 is pushing it for a good system that you should expect to have after spending the money.

The unvented would be best if you can guarantee 30ltrs/min, otherwise you'd be better keeping the tanks and gravity system.

Can't say what is a good price without a survey, so get a couple of quotes after you decide which way you want to go.

The other point is to find a good installer, either from recommendations or past contact.

 

[bm1981]

What about the new mains being 25 all the way to boiler then down to 15. Would this restrict flow back to original?

 

[Agile]

Thats a common misconception!

Think of the water flowing faster through smaller pipes to give the same flow!

Its the dynamic flow rate thats important. I dont think that you have enough information toreach any conclusion!

Nobody can give you a dynamic flow rate over the telephone. It can only be measured at the property!

Tony

 

[bm1981]

Ok had a brain wave. Can I easily convert a wb regular boiler into unvented system, could I relocate the f/e tank to the garage hence zero tanks in loft?

I'm thinking I should stick with hot water storage but can't afford the full unvented set up at the mo so want to be able to upgrade in next couple of years.

Either that or should I go system boiler to start with? Can I run system with vented tank? I have outside mans tap few feet from where boiler wil be situated.