New boiler - noisy

[Ian1981]

I’m looking for some professional / experienced views on whether the following is normal after a recent boiler replacement.

My old system was a Potterton 85 HE (approx. 20 years old), recently replaced with a Worcester Bosch Greenstar 4000 series.

Since the installation I’ve noticed:

• A noticeable “whooshing / flowing water” sound in the pipework when the heating is running
• The noise is audible in multiple rooms (including bedrooms), whereas the old system was essentially silent in this respect
• Radiators do get hot, but the system feels less “instant/aggressive” than the previous boiler
• The house takes longer to feel warm, and thermostats typically sit around ~20°C in normal use

The installer has attended and confirmed the system is operating normally, and described the noise as typical circulation/pump/fan noise for modern boilers and higher-efficiency systems.

I’m trying to understand whether this is:

• normal behaviour when moving from an older non-condensing boiler to a modern condensing system, or
• something that might indicate balancing/flow rate/pump settings/commissioning issues

The system is otherwise working and heating the property.

Any insight from heating engineers or those familiar with Worcester Bosch systems would be appreciated.

Thanks in advance.

 

[denso13]

The new Greenstars are virtually silent when operating, or they should be.

As for time to heat up, do you know what the flow temp for the heating is set at? Condensers do run a bit cooler to allow them to operate efficiently.

 

[CountryFan]

Could be a little trapped air.

 

[richw]

I have had my 2007-installed WB Greenstar combi replaced in 2025 with a new WB 4000 (or maybe even 8000). I changed it because of serious building and relocation works going on at there same time, so it made sense to. The new one definitely makes more noise than the old. I was quite surprised, as I thought I was basically getting there new version of the same (which I had no beef with, other than someone else installed it and it was only serviced when I moved in in 2022).

 

[Johntheo5]

In both cases above, just check that its not something as daft as the flow and return pipes installed incorrectly.

You can also note the set flow temperature and keep reducing it until (and if) the noise subsides.

 

[Johntheo5]

Something else to try, run the CH at its present temperature, then turn the set point (target) temperature down rapidly by say 10C, this will trip the burner but the circ pump will continue to run and the zone(s) valves will remain open, see if the noise remains the same.

 

[richw]

I don't think there is anything wrong with my CH setup. I think the noise is from the fan.