vokera linear 28?

I had the same problem , it was the heat exchanger blocked with sludge etc. We cleaned it out with a bit of wire and a hose and its been fine for 6 months now

Nocorgieneeded
December 2007

PS, if it is the thermistor then the cut out will be due to the highlimit thermostat switch opening, the system temperature should go very high before this happens (watch the front panel temperature guage), normally no big problems running a hot bath if this happens, but problems with very hot water at lower flow rates from basin taps. If the thermister is in place but you suspect it, and you want to be sure, check for high limit switch operation by checking for a voltage appears across the high limit thermostat contacts with a voltmeter when the problem occurs. See manual page 55 for wiring. Be carefull, lethal 240V AC may be present.

cd
April 2007

Does it go from full blast to nothing (ie so doesn't modulate down then cut out), and then back on again?. Could be the air pressure switch. (Pressure differential switch). The switch will not be faulty, however the fan blades, heat exchanger and especially flue venturi probably need a good clean. Google 'Vokera flue venturi temperature cycling' and similar terms for more info. The excel models suffer the same problem.

To download the pdf manual go to www.vokera.co.uk, installer/literature/discontinued products. See page 54 and 55 for wiring of switch, see page 24 for instruction on removing the hood for fan/heat exchanger and flue cleaning. You might want to check the voltages (with a multimeter)across the differential switch when the boiler is misbehaving to be sure of the diagnosis. Be carefully, the voltage could be a lethal 240VAC.


Opening the sealed combustion chamber is potentially dangerous, if you make a mistake in re-assembly then combustion products (possibly Carbon monoxide) could escape into your living space.

Your boiler has presumably not been properly serviced for a couple of years, now might be the time to phone Vokera for a local approved service man to give it its proper necessary periodic service; you should then be able to forget about boilers for another couple of years or so. Avoid generalists, and get someone very familiar with your specific model to do the job quickly and properly, it may work out cheaper and more hastle free in both the short and long term.

cd
April 2007

yes

hi-spec plumbing
April 2007