Central Heating

Boiler hissing/whirring when both CH and HW on

Anonymous user 09/03/2024 - 2.36 PM

Hi guys I have a new boiler (less than one year since installation), vaillant ecotech+ 418. system boiler with header tank in loft. Standard Two zone system, one pump and 2 Honeywell valves ( hw and CH). The boiler seems fine but makes a hissing/whirring noise only when both heating and hot water are on at same time (no noise if I run each individually). Any ideas what this could be? (A gentle bash on side of boiler makes it stop for a few seconds) I presume the heat exchanger is the same for ch and HW? Could it be the water pump can't keep up when both zones require heat? Or could it be low gas pressure when demand is higher? (Gas pipe is narrow, pressure was tested at installation but maybe not with both HW,CH on) Thank you ** Additional Info ** Thank you FIT&SERVE Incidentally, we got a F72 error (Flow and/or return NTC fault). I understand this also points to 'low flow pressure' as you indicated. Unfortunately, my pump (grundfos2) is set on constant speed 3... So I can't make it any faster. I guess this means I have some sort of blockage or poor flow due to dirt... I'll have to look into that. thanks