Hello group, I'm currently having bother with a gravity fed central heating system.
Diverter valve and the thermostat on the hot water cylinder disconnected.
These statements are almost certainly contradictory. Let's assume you really meant you have a fully pumped central heating system...
1. Water in the timer from a leak elsewhere?
2. Loose terminal inside timer?
3. Yes, you can operate the system without the timer, by joining together the wires switched by the timer (it is, after all, just an automated switch). This will eliminate or comfirm the timer. You'll need someone competant with electrics for this, it's not easy or safe to do it by letter!
4. Is the diverter (3-port) valve leaking, and wetting the internal switches?
To blow a 13A fuse will seriously expose your wiring to a fire risk, so stick with the 3A, and don't be tempted to revert to a larger size!
5. Insulation breaking down in the pump windings, usually causes almost instantaneous fuse failure (strictly speaking, the fuse hasn't failed; it's done exactly what it's meant to do!), and you've already eliminated the pump as a failure point.
6. Once had the gas valve coil insulation on a Potty Suprima occasionally break-down on fire-up. It's a long shot, but you can test for that sort of thing by turning the boiler thermostat up and down repeatedly, and seeing if the fuse blows on gas valve switch-on, indicated by an audible click from it - ITT gas valve now replaced with Honeywell as a repair kit from Glowworm.
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