hot water running hot then tepid

[tidders]

After success on this site recently i thought i'd try to resolve my latest problem, my hot water and ch has been on all day, the heating has worked fine but now the hot water runs hot for about 30 secs then turns tepid, turn tap off for a minute then its hot again for 30 secs and so on. I recently (a month ago) changed the three way valve which has worked fine since. Could there be air trapped in the cylinder?
Any help much appreciated.
Tidders.

 

[spraggo]

After success on this site recently i thought i'd try to resolve my latest problem, my hot water and ch has been on all day, the heating has worked fine but now the hot water runs hot for about 30 secs then turns tepid, turn tap off for a minute then its hot again for 30 secs and so on. I recently (a month ago) changed the three way valve which has worked fine since. Could there be air trapped in the cylinder?
Any help much appreciated.
Tidders.

Check that the 22mm expansion pipe is not dipping into the water in the cold water tank up in the loft. As this will cause cold water to syphon down through the hot taps

 

[45yearsagasman]

That's probably not air.Describe your system with more info please.

 

[tidders]

nice one spraggo, the vent pipe was below water level I have lifted it and tied a support to hold it. I presume the overflow is frozen and blocked which also means the ball valve is dripping?

 

[spraggo]

nice one spraggo, the vent pipe was below water level I have lifted it and tied a support to hold it. I presume the overflow is frozen and blocked which also means the ball valve is dripping?

Is the water level above the overflow outlet? if not the overflow pipe is OK. If the ball valve is dripping you have probably used hot water recently or the ball valve needs repairing/replacing.

regards

spraggo