Boiler Cycling

[Fishling]

First post so treat me gently, my dad's boiler has started to cycle on and off for about 3 minutes at a time I have found his 3 port valve motor not to be working and the lever has gone loose, I believe it's in the mid position as the heating and cylinder pipes are both hot to touch would a faulty 3 port cause this cycling ?

 

[0304Driver]

How do you know the 3 port valve motor is not working? If it is just because the lever has gone loose, I am sorry but that does not mean it has, normally it goes loose when in ch, but depends on the valve.
Are the rads hot? does the system have TRVs? Does the system have a room stat?

 

[Fishling]

How do you know the 3 port valve motor is not working? If it is just because the lever has gone loose, I am sorry but that does not mean it has, normally it goes loose when in ch, but depends on the valve.
Are the rads hot? does the system have TRVs? Does the system have a room stat?

Yes it has a room stat it has some trv's and some open rads and the rads are hot, it's a Honeywell valve.

regards

 

[0304Driver]

If the rads are red hot, is the house nice and warm, it could be that you have your room stat set too high, when the system is red hot the return temp can get up to temp very quickly because the rads cant dissapate anymore heat so the boiler keeps firing on/off, make sure the open rads are on and not turned off (at least one) which should be the one in the same room as the room stat. Its worth just doing these simple things to check, if not your best bet is to get someone (Gas Safe) in to check the boiler over for you.

 

[Simon F]

welcome to the forum Fishling.
what speed is the pump set too?
if its on 1 turn up to 2 etc. if this improves things then the pump is showing its age

 

[Fishling]

Hi thanks for the welcome , I have already turned the pump speed pump but this has not cured the problem, I have heard some air cavitating then the boiler fires up would it be a good idea to fit some aav's on the finger vent from the cylinder and any other high points of pipe work.