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Brian, Plumber
Category: UK Plumbing
Satisfied Customers: 845
Experience:  16 yrs. experience as plumber, including full bathroom and kitchen installations.
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I have a danfoss tp5000 type thermostat, but it will not

Customer Question

I have a danfoss tp5000 type thermostat, but it will not light the boiler. If I manually call for heat on the thermostat, still the boiler will not light.
Using a mains tester screwdriver on the boiler, I have a bright light on the live connection, but a very dim light on the switched live connection.
I removed the thermostat and put a fixed link wire between the live and switched live terminals and now the boiler is on all the time, so I obviously know the boiler is working.
How can I test the thermostat as the display is as expected, but it will not light the boiler?
Submitted: 1 year ago.
Category: UK Plumbing
Customer: replied 1 year ago.
Expert:  Brian replied 1 year ago.

By checking the switched live to the boiler you are checking the thermostat.

The display can work fine but still not allow a current to pass through the unit when its supposed to.

I am not sure its possible to test these unless you can rig up a unit so that you can get a meter into the switched live prong while activating the stat.

My advice would be to buy a new one as im pretty sure its broken. If you buy it from a diy store you can always take it back if im wrong.