Vokera Boiler Issue

[tjd100]

Our Vokera Linea 28 has been in our flat since we bought it (9 years ago). Just before Christmas the DHW Heat exchanger was replaced (full of sludge). Has been working fine until the weekend when started cutting out on demand from the shower. Like the heat exchanger problem allows the boiler to get to temperature before shutting down, cooling down and firing again. However doesn’t appear to be the same problem as the water temperature stays low (75 max).

We have the DHW thermostat set to maximum (always have) and it now cuts out when the water going to the shower reaches 55 degrees. However if the thermostat is turned down it then cuts out at a correspondingly lower temperature - i.e. set to half it will cut out at 48 degrees.

I’ve been unable to find a similar problem discussed on this forum (and apologies if I’ve missed something obvious). Any ideas/thoughts much appreciated.

tom

 

[Masood]

Was the whole system properly powerflushed when the hat exchanger was replaced? If not done thoroughly it's possible that remnants of sludge have started to choke up the new heat exchanger.

 

[tjd100]

Yes, the system was flushed and before the heat exchanger was replaced the temperature would jump to over 90 degrees when shut off. Now it's never much higher than 70 degress (75 max).

 

[on31ll]

did you see them flush the system ? was inhibitor added afterwards ?

 

[tjd100]

Yes and yes. I'm not qualified to judge competence/diligence but seemed to know what they were doing...

 

[on31ll]

Well you need a gsr ! Bleed the radiator and see what colour the water is ?

 

[jtsplumbing]

Is the boiler showing any error coad's (Flashing red) ?

 

[on31ll]

And it only happens with the shower ?

 

[jtsplumbing]

If other outletts are ok then the fault must be with the shower , are the spray holes in the shower head blocke'd, remove head and try shower just useing hose , is same thing happining ???

 

[tjd100]

Good idea, I'll check when I'm home.

If I run the taps the temperature on the boiler never goes above 52 degrees and therefore doesn't cut out (assuming the thermostat on the boiler is set to max). I had assumed the TMV in the shower was restricting the flow of hot water hence the increase in temperature. However doesn't explain why the boiler is cutting out as I assume it would moderate the flame to compensate...

Is 55 degrees a normal shutdown temperature?