Boiler running while heating/ water timer off

[ridgewalker]

I have noticed several times now that my gas boiler is fully fired up and running hours after the central heating and water clock should have turned off. We have an electronic control timer and on inspection see that nothing should be on, yet the boiler is still running. I am not aware of any anti frost settings and besides it has even been running when outside temperatures have been at 10C.

Has anybody got any ideas? I cant understand why the boiler is on when no signal should be getting sent from the timer/controller

 

[simond]

It's usually caused by a seized motorised zone valve.

 

[Tipper]

You should be able to change just the motor head on the valve.

 

[ridgewalker]

Thanks that sounds hopeful. By moterised valve are you referring to the 3-way valve in the loft? I had one of these seize a few years ago and could only get hot water and no heating.

Are you saying that a similar thing may have happened and the boiler just stays running. I believe there are two of these valves in the loft so will take a look.

 

[ianniann]

Or ... the water diaphragm has stuck and the boiler thinks you are running hot water.

Do the radiators get hot when the boiler is stuck in this mode?

 

[ridgewalker]

No the radiators do not get hot. I noticed it came on today at lunchtime the clock had switched the water and heating off at 9am. When I checked at 10am the boiler was off so something caused it to switch on again at lunchtime even though the control timer was off.

Assuming it was the zone valve, would running the hot water cause the tank to cool down and therefore the boiler switch back on? Or is this symptoms of the water diaphram?

Incidentally since reading the responses I tried manually moving the lever on the zone valve and the boiler came on. It did not automatically move back which I had expected it to.

 

[ridgewalker]

Changing the moterised valve did not work. I have also tried turning down the room stat and the water stat (on the tank in airing cupboard). As soon as the water in the boiler cools down sufficiently it bursts back into life even with the water and heating in the off positions. My Clock/timer is a Potterton EP300 if that is any help.

Could it be the EP3000 sending a rougue signal to the boiler to fire up or perhaps some electrics in the boiler that do not work.

 

[ducatikid]

EP's had a habit of staying on when the switch/lever was set to off , but you would notice the red indicator alighted. What type of boiler do you have? You mentioned you had 2 valves (motorized) one of which was a three way valve , was this an error , and you have 2 two-ports?

 

[ridgewalker]

The 3 port wa an error on my part, I have two 2 Port valves. The Boiler is quite old but have been told it was good in its day. Its a Potterton NETAHEAT ELECTRONIC.