I recently had 3 new radiators fitted and when the system is running there is a hammering noise which randomly starts on one of the radiators. I have checked the valve and it has been fitted on the wrong side of the radiator. When I called the plumber he said the valve was not causing the problem as it was a 'multi flow valve' and could be fitted on either side of the radiator. Is this correct and if so how can I check if the valve is indeed a multi flow valve?