How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Plumberpro Your Own Question
Plumberpro, Mechanical Engineer
Category: HVAC
Satisfied Customers: 634
Experience:  Over 20 years experience in plumbing heating and gas
Type Your HVAC Question Here...
Plumberpro is online now

I have a Greenstar Si compact installed 2 years

Customer Question

Dear Sir,
I have a Greenstar Si compact installed 2 years ago. The problem is that the pressure went down several months after installation and the water in the bathroom shower became very weak or even no hot water activated. We last time asked a technician to come to help to adjust the problem.
But the pressure went down again last week, I therefore would like to know if there is a way that I can adjust the pressure by myself where pressure become too low?
Best regards
email :***@******.***
Submitted: 2 years ago.
Category: HVAC
Expert:  Plumberpro replied 2 years ago.
Hi . these have an internal filling loop. Slide the panel out underneath the boiler .there should be a filling key . a white plastic key with rubber o ring .
Look for the hole it slides into under the boiler . push the key up and into the hole turning to lock it into place. There are two taps either side of the key open these ( turn off if water leaks ,as this means the key isn't inserted properly ) open taps till repressurised then turn off . sounds complicated but easy once you get the hang of it
Customer: replied 2 years ago.

Dear Sir,

Thank you for your answer, but I still cannot find the hole or the key at the boiler underneath as you mentioned.

at the boiler underneath there are two big pipe (around 1" or over in diameter) in parallel with the boiler panel face width, there is a plastic ring in black color just next to one of the big pipe, a screw appeared at the end of the ring. I try to turn this ring with my fingers but it seems it is firm.

If possible, could you send me a drawing or a photo to show the right place? I have doubt that I found the wrong ring.

The Boiler is:

WORCESTER (Bosch Group).

Greenstar Si Compact.

Wall Hung RSF Gas Fired Condensing Combination Boiler.

Model :WORCESTER 25Si Compact.

Purchased in year 2014.

Thank you very much your help again.

Best regards


Expert:  Plumberpro replied 2 years ago.
Hi , yours may not have a built in filling loop. Google 'filling loop images to see what filling loops look like . they are a flexible hose that connects the mains water to the central heating pipes to fill the system with either one or two taps at each end . open these and watch the pressure gauge to turn off at around 1.3 bar . the filling loop should be under the boiler on the pipework , however I have found them under sinks , in lofts orthe old hit water tank cupboard.
Your boiler pressure has no relation to the water pressure that comes out of the taps. It is a separate circuit.if you have water tap pressure issues then that is a different issue.
First you need to check your water flow rate .your boiler does 9 litres per minute at a 40 degree temperature rise for hot water .