As our boiler is gravity fed, my T503's on low pressure should be running for a very long time - but as some of them were probably installed in the early-mid 90's and only give a few seconds I suppose they have just died of old age
. There appears to be only one model of the T503 - is this right ? I don't see how these work - is it friction from the rubber seals ? - main thing being will they just need a service pack T503/750 ( 936.75) or a cartridge assembly 902.79 to restore them For future reference - presumably then the "flow restrictor" ( part 146.04) simply governs the amount of water going to the shower head ?