Worcester Bosch Cycling Issue

[Jpm757]

Good afternoon everyone, I am hoping you may be able to help me. I have a Worcester Bosch 19/24CBI boiler and it keeps cycling. When trying to heat the hot water (same for heating) the boiler is off more than it is on and thus unless timed for a very long time never gets the desired outcome. In essence it was on with the burner lit for around 18 minutes in an hour and no burner lit for 42 minutes in an hour. Whilst the burner was off, the fan and pump remained running. The pump is quite new and I am sure has good flow. Below is the timings of the on and off cycling of the boiler covering an hour for info:
On 4:41
Off 5:57
On 2:47
Off 4:48
On 1:46
Off 5:14
On 2:10
Off 5:59
On 2:07
Off 6:46
On 2:18
Off 9:07
On 2:17

From time to time - every few weeks it also locks out and I need to reset it by turning the dial to the left and back again.

Does anybody have any idea what may be causing this cycling issue or locking out please? All ideas and theories appreciated as it’s an old boiler and I do not have a lot of money to throw at it.

 

[ShaunCorbs]

Could be a few things, sensors , pump can’t pump the water away fast enough and maybe hex is dirty etc

 

[Jpm757]

Hi ShaunCorbs, thanks for the reply. The pump was replaced in case it was the cause. It has 3 speed settings and it makes no difference to the cycling on setting 1 or 3. Which sensors may be at fault? Being old it’s quite basic any guidance would be appreciated in where to start looking. Sorry for the dumb question, but what is the hex?