Vokera Linea Max - Hot Water Not Very Hot

[EViS]

We have a Vokera Linea Max combi which has recently developed a fault whereby the hot water intermittently isn't always very hot. Every now and again, a bath of water or shower runs lukewarm or when turning a hot water tap on, it takes longer than usual for hot water to run.

The central heating functions fine and the pressure is at around 1.8 bar.

Any idea what could be the problem here and/or what we should try cleaning/testing/replacing first?

 

[petertheplumber12]

Can you be a bit more specific about the hot water behaviour? For example does the hot water run quite slowly know compared with a few months ago, or does the boiler switch on and off while trying to produce hot water, you need to look at boiler while running hot water.Or is it behaving different to either of those?

 

[EViS]

The water flow seems to be the same as before, and the boiler does not switch on and off whilst running hot water. However, the temperature does not seem to rise about 49 degrees, despite the dial being at max. As soon as the water flow is switched off, the temperature momentarily jumps to around 91 degrees.

I'm unsure how this boiler behaviour differs to previously.