No hot water is one of the most common calls I get about unvented cylinders. Often it's something simple, and there are a few things you can safely check yourself before calling anyone.
Got a Megaflo or unvented cylinder problem in Orpington, Bromley or south east London?
I'm a G3-qualified engineer and service and repair all makes of unvented cylinder. Cylinder service £140, no VAT to add.
Safe things to check first
- Is the boiler or heat pump working? If your cylinder is heated by a boiler or heat pump, check it's on, has power and isn't showing a fault code. If the heating isn't working either, the problem is probably the boiler or heat pump, not the cylinder.
- Is the hot water switched on? Check the hot water timer or programmer, the hot water setting on the heat pump controller, and that the clocks haven't changed the schedule. After the clocks change, timers are often an hour out.
- Has anything tripped? Check your fuse board, and the switch or spur for the immersion heater.
- Is the cold supply on? If the cold supply to the cylinder has been turned off, you'll get little or no water from the hot taps at all.
Don't open the cylinder covers or touch the safety valves. Those checks need an engineer.
The common faults behind it
1. Motorised (diverter) valve stuck
On boiler and heat pump systems, a motorised valve sends the hot water to either the cylinder or the radiators. If it sticks on heating, the cylinder never gets heated.
2. Cylinder thermostat or sensor fault
If the thermostat or sensor isn't reading correctly, the system thinks the water is already hot and never calls for heat.
3. Immersion heater failure
If you rely on the immersion, or it’s your backup, the element or its thermostat can fail. A blown element is a common fault on older cylinders.
4. The overheat cut-out has tripped
Unvented cylinders have high-limit cut-outs that switch off the heat if the water ever gets too hot. If one has tripped, there's a reason. It needs finding before it's reset.
5. Heat source fault
A boiler or heat pump fault will stop the cylinder heating even if the cylinder itself is fine.
Lukewarm rather than cold?
If the water is warm but not hot, it's often the settings rather than a fault: the cylinder temperature is set low, a blending valve is turned down, or the hot water isn't scheduled to heat before you need it. See my post on why hot water can feel cooler than the cylinder says.
Need an engineer?
I'm G3 and heat pump qualified, and work on unvented cylinders, heat pumps and their controls across Orpington, Bromley and south east London. If it's not a simple fix, give me a call on 07717 846247.
Need it looked at?
If your cylinder is losing pressure, dripping at the tundish, making noises or not giving you hot water, I can come and find out why. Annual cylinder service £140, or £285 with your heat pump. No VAT to add.
Cylinder getting on a bit? If it's 15 years or older and giving you trouble, a replacement often makes more sense than repeated repairs. Unvented cylinders supplied and fitted from £1,550.