British Gas 330+ CH Output Limited to 10KW

[jsr2002]

Just moved into a new house. Noticed the rads weren't that warm. Checked the smart meter and noticed that despite the boiler (British Gas 330+) being 30KW, the smart meter only ever shows us burning 10KW.

Thought to myself - the boiler has obviously been range-rated down to its lowest setting (10KW). Checked the setting, but find it's set to the manufacturer default of 18KW.

Bit stumped now, was convinced I'd find it range-rated to 10KW as that's all it appears to be outputting (according to smart meter and as suggested by the lukewarm rads).

Anyone got any ideas about what might be limiting the boiler to only giving us 10KW? It's not range-rated down to that (it's set at 18KW)

One other potentially important thing - after starting the CH, occasionally (intermittent) I get a buzzing/vibrating noise for approx 15 mins. It eventually dies down, but it doesn't sound too healthy for that first 15 mins or so. Intermittent comes and goes.

Heating Engineer coming to look at it in the New Year, wondering if anyone has seen this before though and might have some idea what it might be. Thanks in advance for any thoughts/ideas, really appreciate any input folks might have!

 

[jsr2002]

A few more things -- the flow temp is set to 70 and the readout on the front of the boiler (presume measured at the return) measures somewhere around 45-50.

The temp in the house (during this cold snap, before the heating turns on) is ~11 degrees celsius and the target temp on the Hive is set to 18 degrees.

So, the system should in theory be calling for more heat and output from the boiler. It's not as though it should have any reason to modulate down to 10KW that I can see,

 

[ericmark]

Boiler modulation can be controlled by electronics with things like OpenTherm thermostats, or temperature of return water, so if any radiator has not had the lock shield set, then it can return hot water, which will turn down boiler.

Once my TRV and lock shield were set correctly, the boiler modulated so radiators did not get that hot, but rooms at temperature set.

Remember the on/off thermostat, is to stop boiler cycling, not to control temperature.

 

[jsr2002]

And another thing - I should probably be careful with the term "modulate". The little flame icons on the front show "max burner" (5 flames) even though it only appears to be giving us 10KW and its range rated for 18. Hence it believes it's going at full-burner.

Yet another part to the riddle!

 

[MeldrewsMate]

Have your gas fitter ensure that the gas valve inlet filter is clear. A weak burner ratio could cause the noise you described.
For your part, can the boiler display the actual fan speed? Does this match the calculated fan speed (the demand speed)?
Have you tried turning the max. power down to the 10kW minimum? Does this reduce the power consumed as read from your smarty-pants meter (they don't update the display instantly, so be patient)?
Conversely does turning up the max power to 30kW cause the fan speed to increase? Does it exacerbate the noise? Does it cause flame loss errors?

 

[Twenty Four]

I was experiencing exactly the same symptoms as yourself and it is apparently, after diagnosis, a blocked heat exchanger. My boiler ran like that for a few days then eventually failed to start up. It is being replaced on Friday.

 

[jsr2002]

@MeldrewsMate thanks for the good ideas. Just checked the fan speed now (d.33 and d.34 under the diagnostic menu as described in the manual).

target value (d.33) is 309
actual value (d.34) is 309

Looks like it's getting to target.

 

[jsr2002]

Thanks for thoughts @Twenty Four. Hope that fixes it for you and isn't too expensive. Let us know how you get on once it's replaced.

 

[Johntheo5]

Check the menu for a d parameter that sets the max boiler temperature on CH.

A few more things -- the flow temp is set to 70 and the readout on the front of the boiler (presume measured at the return) measures somewhere around 45-50.

The temp in the house (during this cold snap, before the heating turns on) is ~11 degrees celsius and the target temp on the Hive is set to 18 degrees.

So, the system should in theory be calling for more heat and output from the boiler. It's not as though it should have any reason to modulate down to 10KW that I can see,

Boiler output is proportional to the fan speed, so 10kw @ 3090RPM should equal 18kw @ 5562RPM. but equals 9270RPM @ 30kw, no way I'd say so maybe blockage somewhere??.

@MeldrewsMate thanks for the good ideas. Just checked the fan speed now (d.33 and d.34 under the diagnostic menu as described in the manual).

target value (d.33) is 309
actual value (d.34) is 309

Looks like it's getting to target.

 

[MeldrewsMate]

@MeldrewsMate...Just checked the fan speed now (d.33 and d.34 under the diagnostic menu as described in the manual).

target value (d.33) is 309
actual value (d.34) is 309

Looks like it's getting to target.

Then you have eliminated a fan error as one possibility.
I am reminded of an old adage: eliminate the impossible, and what is left is surely the more probable.

Have you tried the other suggestions, ie turning up the max power to 30kW? Does this increase fan speed further? Does an increase in fan speed cause flame loss alarms or more grumbling noises from the boiler?

 

[Johntheo5]

Check the menu for a d parameter that sets the max boiler temperature on CH.

 

[Twenty Four]

Thanks for thoughts @Twenty Four. Hope that fixes it for you and isn't too expensive. Let us know how you get on once it's replaced.

As previously mentioned, I had exactly the same symptoms as you and today my heat exchanger was changed and the boiler is fine. In fact it's better than it was so I suspect the fault was slowly building up over the last few months.