vaillant thermocompact

[ambrosia]

got an old late 80s vaillant thermocompact (i think this is the right one)
http://heatingsupplies.com/linked/b...vc gb 182eh 242eh 282eh 182eb 242eb 282eb.pdf

1st time i went there i found that the pipework was well undersized, as i recall working pressure was a massive 4 mbar down from the meter to boiler (3mbar on the hob) and the burner pressure was over 2mbar below the 6.8 it should have been getting

replaced all the pipework and at the same time i also changed the gas valve, i suspected there was something else wrong, no matter how much i played with the old gas valve couldnt get the burner pressure up

now boiler fires up, goes for a little while then turns itself off and wont come on again till reset, doesnt matter if you turn temp up. burner pressure is still down

i suspect its the overheat stat or thermistor flow sensor, possibly could be pcb

however given the amount of work i've alread done and that i've probably put a new gas valve in unnecessarily, i absolutely can not afford to f### this up.
Any advice or sugestions gratefully received

 

[Nostrum]

pressure differential dropping out maybe, resetting gives the pump a shunt enough to open again?


Also take a look at page 29 of the manual you just linked.

 

[ambrosia]

whats best way to test pressure differential

 

[Nostrum]

continuity through the switch on demand.

 

[thereisawizza]

There is also a diaphragm pump that takes the gas to full rate. If this has failed will go to lockout and push black switch out...