gas rates on boilers

[desrob]

when doing gas rates,my boss always told me to run the hot tap at full rate to ramp the boiler up to full rate, giving you a max heat input reading,so when you put the boiler in service mode is it working on full rate, ch or dhw or both the mi give different heat input figures always higher on dhw side, so if running the tap ,do i correspond my figure with that or when in service mode do i use ch side (condensing) figure.i hope you understand what i am asking thanks for your help

 

[Reg Man]

You can turn on all the hot taps, but if it goes into modulation it will give false reading. Therfore best follow MI's and set it into max rate on the service buttons. If your doing combustion analysis on zero governed boilers you should do this too, and also at minimum rate.

 

[GrahamM]

As Reg Man mentioned, follow the MI's, but even in service mode some boilers can be a pain to work with and will modulate down before you can get the gas rate etc. and you have to revert to running the hot tap. Older people who have the heating on full bung when you arrive having the boiler in region of its max operating temp already, are the worst culprits.
I try stick with MI's as much as possible but running hot tap is only option at times.

 

[tamz]

Some put the divertor valve into mid position when you enter service mode so running a tap helps to stop it modulating down.

 

[desrob]

what about the difference in heat input figures, always higher on dhw side, so your running the boiler in service mode and you have got the hot tap running gently through the boiler,should my figure correspond with the lower condensing heat input figure or the higher dhw figure.

 

[noleaksihope]

the heat input figure for ch is usually the max rating in normal operation , ie not in service mode .
some 35kw combis will give you 35kw on dhw , but only max 28kw on ch in normal operation . so your figure for service mode corresponds with max input for dhw , your figure for ch is max rating in normal ch operation .