glow worm CXi 30

[shaun123]

hi i have a cxi 30 it will not heat the water past 50 deg on the C/H there must be an easy fix for this?
please help!!

 

[kevplumb]

turn the boiler stat up

 

[advancemaintenance1]

just a thought im a joiner but are your trv s turned up full

 

[shaun123]

thanks, yes, i've cured it, there is some jumpers on the circuit board, i altered these one at a time and now it works at 85 deg!!

cheers

 

[mickyg]

turn it down then. 85 is not a good temperature for a condensing boiler. Try 60.

 

[shaun123]

ok. why is 80-85 bad? as the litrature referes to this temp, when it was at 50 it was poor, this boiler has had multiple problems over the past years, and has had most parts replaced
no i dont know who you think you are!, but am greatful for the advice, but would like to know the details behind the seting

cheers

shaun

 

[kevplumb]

trick is to keep the return temp down so the boiler is condensing

 

[mickyg]

ok. why is 80-85 bad?

because it won't condense and therefore will not be efficient. Set the temperature at the lowest temperature it will keep your home warm. If that has to be 80 then your radiators are too small or not working properly.

 

[shaun123]

The temperature of the central heating water can be adjusted by turning the central heating water temperature
control to desired setting between 1 'Min' and 'Max'. Maximum setting is appoximatly 82°C.

this is a quote from the manual

this is what the boiler is reading, why is this bad, if it designed for this, the design and economy ratings are based on a 75 deg c average system temp
i'm still confused as to why this operating temp is bad

the delta t accross the radiators is based on a 85 deg operating temrature too

 

[mickyg]

because it won't condense! For your boiler to condense the return temperature needs to be lower than 55c, the lower the better. Most systems are set up for a delta T of about 11c. When switching to a condensing boiler the installer should try and set the system up to increase the delta T to nearer 20c, however many installers don't bother, and for those that do its not always possible. So if we assume you have delta T 11c then anything over 66 on the flow will mean greater than 55 on the return therefore no condensation and less efficiency. Turn it up to 80 if you want, your gas bill.

 

[shaun123]

thanks,

why does the manufacture not state this in his installation manual, but netherless, the out put temp of the water is arround 75 deg with return arround 59 so to gain the efficiency if i reduce to 70 i should be lower than 55

if this is so critical to the effiecy, why are these boilers rated as A if they can operate outside this range? i smell a rat! means bigger radiators to transfer the heat, as there is less energy contained at 60 deg that 80 also means more pipe, more water, larger expansion larger boiler as it will not put out is kw rating as this is at 82 deg looks like a stitch up, but i know nothing about boilers

still confused!!

 

[kevplumb]

you are confusing temp with heat

two different things

 

[shaun123]

Temperature with heat? when the system pressure and volume are constant, which they are, apart from a minor rise in pressure the temp is the only changing factor, so less temperature less heat (kw), where did you go to college?
I presume by heat you mean energy and not something else

 

[kevplumb]

well seeing as gas burns at a constant temp 1930 c

so less temperature less heat (kw), where did you go to college?

try heating your house with a 1 kw boiler then smartass

 

[shaun123]

you would get less temp with a 1kw as i said temp is directly related to heat the heat emitted from a radiator or heating panel depends primarily on the temperature difference between the radiator and the surrounding air.

The heat emission can be expressed as:

P = P50 [ (ti - tr) / ln( (ti - ta) / (tr - ta) ) 1 / 49.32 ]n (1)

where

P = the emitted heat (W, J/s)

P50 = the emitted heat with an temperature difference 50oC (W). In general radiators are dimensioned1) for a middle temperature of 70oC and surrounding temperatures of 20oC (a difference of 50oC)

ti = water temperature inn (oC)

tr = water temperature out (oC)

ta = surrounding air temperature (oC)

n = constant describing the type of radiator (1.33 for standard panel radiators, 1.3 - 1.6 for convectors)
utut and the energy transfered

so if we go for the low c/h water temp as advised the heat transfer is less the radiators are operating below their design point the system is less efficient and needs to run for a longer time to achieve the temp rise in the room(s) so is less efficent i think

still confused, there seems to be lots of heresy enginnering going on with little technical reason