Oil Boiler - Won't Start Hot straight away!?

[JohnnyTooSharp]

Hi, this is about my own boiler. I'm a new-ish plumber but no boiler experience.

It's a...... Worcester Greenstar Heatslave External 18/25 Oil Boiler

It had a new burner and was serviced at the end of December 2024, and I've just re-pressured the boiler and it's expansion vessel to try resolve the issue.

BUT, for a few weeks now, when we run the shower, it comes on warm/hot for a few seconds then turns cold. Then we have to keep turning on and off, getting hot then cold water each time. It only stays hot after maybe half a dozen times, sometimes more. It's getting quite annoying now! No other plumbing in the house has changed.

Anyone know what the problem is and the solution?

 

[ShaunCorbs]

Could be diverter or store ntc

Does the boiler fire ?

 

[JohnnyTooSharp]

Does the boiler fire ?
[/QUOTE]
Well it does, but on and off for about 5-6 attempts until stays on!

 

[JohnnyTooSharp]

Does the boiler fire ?
[/QUOTE]
Well it does, but on and off for about 5-6 attempts until stays on!

 

[JohnnyTooSharp]

Is it worth changing the diverter and ntc then? Do I need my boiler guy or could I just do it? How much am I looking at roughly for the parts?