Boiler noise

[Peach533]

We have a Worcester Bosch greenstar boiler approx 5 years old. During the summer we have fantastic hot water no problem. During the colder months when the central heating is on we still get fantastic hot water and great central heating but sometimes when we turn the hot water tap bath/shower etc.... The boiler makes a noise like an aeroplane taking off! We then notice that the pressure has dropped and we need to top it up. It holds the pressure for a little while but then gradually drops again. This problem only seems to happen when the central heating is on, it happened earlier in the year when the heating was on and then during the summer the pressure remained fine?
Any ideas what the problem could be before I get someone out??
Thank you

 

[SimonJohns]

Sounds like you have a failed part

Relatively cheap. And shouldn't take a good GSR to do

Where in the country are you. Perhaps someone on here could help you out

 

[Peach533]

Thank you, excuse my ignorance but what is GSR?
We are in west london

 

[WHPES]

Gas Safe Registered Technician

Gas Safe Register | Ensure your gas engineer is registered.

 

[Peach533]

Aha thank you.