https://www.grantuk.com/professional/support/product-support/solar-thermal/troubleshooting/what-to-check-if-system-is-losing-pressure/
What to check if the system is losing pressure? Solar thermal troubleshooting support - Grant UK
Troubleshooting support for heating engineers if there is a loss pressure on a Grant Solar Thermal system.
solar thermal troubleshootingchecksystemlosingpressure