Advice on replacement boiler/cylinder pse

[pe2dave]

Non plumber seeking advice.


17 year old gas boiler, odd cylinder (coil to rads/ tank body from boiler?).


Looking to replace boiler and tank and I don't know what to expect /
ask from plumbers estimating?


Looking for an efficient boiler (Vaillant/Worcester Bosch chosen).
Current boiler is 50000 btu (15 kW?) so I'm expecting similar
modern boiler would suffice - the old one worked OK. Largely
decided on a non-vented cylinder.


13 rads, 2 bathrooms so combi seems out of the question.


I seem to learn something from each plumber - is there a check list
I could use anywhere? Mainly regs related. E.g. last one pointed out
the necessity of running an ?overflow? from the cylinder in case
of over pressure. No one else mentioned that.


Re the boiler, one said over 15kW I need a 22mm gas supply! Is it the
boiler rating that determines this or the gas pressure? I have a 15mm
supply which one guy measured at 21mbar which he thought OK. What
determines the gas pipe size needed? Another run of pipe is another
expense.


Any advice appreciated.

 

[Ermintrude]

Your gas supply may be suitable for the smaller boiler but can't comment on larger one with out seeing job and making calc.

Unvented needs a specific fall and dia of COPPER pipe not overflow. It's


U have not mentioned what your static and dynamic water pressure is and the Median flow rate.

You will need a balanced cold also. But your installer will know all about this from his unvented training. (He will have a card)

I would say a 937 valliant would suffice and probably work better than a poorly fitted uvhss.

 

[Killy Bing]

Of your chosen boilers
i would suggest the vailliant

i won't start on the better brands

with the gas pipe it depends on how its fitted, the run length, what else is connected too and the amount of gas needed.
we can only have a certain pressure drop between the meter and appliance while running all appliances full tilt.
the engineer will work this out (or atleast he bloody should)
15mm might surfice depending on these.

as ermi says you can go for a larger storage type combi or an unvented (subject to dynamic pressure and flow rates)
no point installing an unvented if you can only achieve a combis preformance.
at the same time if mains is poor it could even be an option to remain vented.

Again the engineer should check both of these!

The next thing is pressurising the central heating or not.
pressurised is better for the system + boiler but can promote leaks to show up initially.
its not advisable if you have pipes in solid floors.

Are you open to recieve quotes from forum members?

 

[Ermintrude]

1 million dollars but £499 boiler scrappage? Oh you've had a BG quote already???

 

[AWheating]

your unvented cylinder will prob need more kws compared to your old cylinder so your boiler size may need to be bigger.

 

[pe2dave]

Your gas supply may be suitable for the smaller boiler but can't comment on larger one with out seeing job and making calc.

What factors determine the calculation please?

Unvented needs a specific fall and dia of COPPER pipe not overflow. It's
U have not mentioned what your static and dynamic water pressure is and the Median flow rate.

Sorry, I don't understand that statement

You will need a balanced cold also. But your installer will know all about this from his unvented training. (He will have a card)

I would say a 937 valliant would suffice and probably work better than a poorly fitted uvhss.

Balanced ??? cold? What's balanced against what pls?

uvhss? Not found in Google.

Dave

 

[pe2dave]

with the gas pipe it depends on how its fitted, the run length, what else is connected too and the amount of gas needed.
we can only have a certain pressure drop between the meter and appliance while running all appliances full tilt.
the engineer will work this out (or atleast he bloody should)
15mm might surfice depending on these.

Thanks. Gas fire and cooker. Piping under concrete so no idea of run length. One guy quoted pressure(??) as >21 millibar. Guessing pipe length + other devices determines gas flow capability? What I'm not keen on is the guy coming up afterwards and laying fresh 22mm pipe. What must the pressure be at the boiler for say an 18kW boiler?

as ermi says you can go for a larger storage type combi or an unvented (subject to dynamic pressure and flow rates)
no point installing an unvented if you can only achieve a combis preformance.

Sorry, not understood. AFAIK a combi requires much more gas pressure and bigger boiler. One guy basically said the drop in
water pressure when two showers or dishwasher on will make it a no go so I'm discounting a combi[/QUOTE]

at the same time if mains is poor it could even be an option to remain vented.
Again the engineer should check both of these!

What definition of 'poor' please?

The next thing is pressurising the central heating or not.
pressurised is better for the system + boiler but can promote leaks to show up initially.
its not advisable if you have pipes in solid floors.

Which I have (House new in '96).
Thanks. I'm assuming you mean pressurising above mains water pressure?

Are you open to recieve quotes from forum members?

Atm, no thanks, I'm confused enough with the ones I've received!

 

[pe2dave]

your unvented cylinder will prob need more kws compared to your old cylinder so your boiler size may need to be bigger.

Noted, thanks. Two factors occur to me here, new boiler should be more efficient than old, ditto cylinder. Should this not offset increase in heat (and why please? Better insulation, 'right way round' etc, I find that puzzling).

Dave