Combi gas rate

[Frog67]

Evening all.
having not renewed my Gas Safe registration since 2008 i am now about to retake my CCN1 this Tuesday.
After 4 days of class and practical study i feel like my brain is about to burst.
So sitting at home today with my head in my books i thought "i know, I'll do a gas rate on my combi and compare it with the MI's."
After pulling out the instructions it dawned on me that they show the Max Input for Hot water (KW) and max input for heating (KW).
Now I'm 99.9% sure that you take the gas rate for a combi from the H/W but to be honest ive got so many figures flowing through my brain at the moment i thought I'd ask on here rather than than ploughing back through my books and notes.
Its funny how i can still recall things like CSA's for gas fires and yet the above has completely left my mind lol.
Any advice would be greatly appreciated.
Frog

 

[ShaunCorbs]

hot water or service mode

 

[Frog67]

Thanks Shaun,
just for clarification i had the boiler in service mode but what threw me was the fact that the MI's show a max heat input for DHW and a max heat input for the CH. I took the gas rate and compared it to the DHW not the CH.

 

[Scott_D]

What boiler?

 

[REDSAW]

whats a csa??????????/

 

[Frog67]

Redsaw, Cross sectional area dimensions for flues and terminals etc.
Scott, my boiler is a Greenstar 24.
Its not what the individual boiler is, its the standard procedure for calculating combination boiler gas rates, IE do you use the heat input for the DHW or CH from the MI's or data plate when your carrying out the gas rate calculations from the meter.

 

[Billy Bob Bob]

Martin its Cross sectional area,tape inside the flue measuring its size

 

[Billy Bob Bob]

Redsaw, Cross sectional area dimensions for flues and terminals etc.
Scott, my boiler is a Greenstar 24.
Its not what the individual boiler is, its the standard procedure for calculating combination boiler gas rates, IE do you use the heat input for the DHW or CH from the MI's or data plate when your carrying out the gas rate calculations from the meter.

as shaun said dhw or service mode are you using short hand or a app,as apps are now regarded as acceptable by GSR

 

[Frog67]

Thanks for the replys.
what threw me was the fact that the manufacturers Instructions give a max heat input for the DHW and a max heat input for the CH, the DHW input was the highest rating in KW. i put the boiler in service mode and ran the hot tap to stop it modulating.
ive been using short hand and the gas rate sheets as ive been told apps are not allowed in the assesment

 

[ShaunCorbs]

Thanks for the replys.
what threw me was the fact that the manufacturers Instructions give a max heat input for the DHW and a max heat input for the CH, the DHW input was the highest rating in KW. i put the boiler in service mode and ran the hot tap to stop it modulating.
ive been using short hand and the gas rate sheets as ive been told apps are not allowed in the assesment

easy way just take the biggest no out of the two and your right hot tap on and if got a service button switch that on as well

 

[Frog67]

Thanks Shaun

 

[REDSAW]

oh right. only had my fires for a month.lol