Valiant Boiler - Not starting after system been drained

[padsmith70]

Have a Valiant combi boiler - have just drained the system. Changed a radiator for a new one add added a Thermostatic radiator. Have re-filled system to 1.5Bar. Gone to each radiator and opened valve until all air is released , then repeated increasing bar to 1.5 Bar on the system.
On turing on the water or heating, the fan seems to start up and the pilot light is alight but it doesn't kick into heat up the water. The hot water tap flows happily, so no blockage in the system and all radiators are all air free.
When I switch off the cental heating switch or hot water tap, you hear as if there are bubbles floating to the surface inside the heating unit.
Any ideas ?
Do you require the actual model of the boiler to help identify ?

 

[kevplumb]

Do you require the actual model of the boiler to help identify ?

always helps

make sure the auto air vent usually on the pump is open

 

[padsmith70]

Ok, do you have any access to a diagram showing where that is ?
When I get home will provide model number of boiler.

Thanks

 

[padsmith70]

It is a Vaillant vcw-sine 18 T3WFH

Combined Heater Cat 1 Type C

Hope this helps ...appreciate your feedback..

 

[Agile]

If you were stupid enough not to turn off the boiler when it was drained and somebody used a hot water tap then the boiler may have fired up with no water in it.

There is a resettable overheat stat on the right hand side of the metal circuit box under a black rubber cover.

After turning off the power you can push back in the little button by pressing on the rubber. Its difficult to reach if you have big hands!

If the pump has been running dry then the impeller may have melted and fallen off!

Tony

 

[kevplumb]

It is a Vaillant vcw-sine 18 T3WFH

Combined Heater Cat 1 Type C

if you have killed a sine 18 danny will come and get yer

 

[Gasguru]

Auto air vent on the back of the pump possibly blocked.

Any trapped air in the boiler may stop the hydraulic gas valve operator from working.

If you are very carefull the air vent can be renewed - but sometimes the brass is so old it crumbles.

Alternatively carefully use a pin to manual bleed air from the vent.

 

[Agile]

The AAVs never normally block because they continuously leak and that keeps the flow path open.

Good point about the air in the system though. It will clear naturally if the heating is left on for a day or two.

If you have to get it working on the spot then the combustion chamber has to be removed ( CORGI job ) and the air beed nipple at top right of primary heat exchanger has to be opened to expel trapped air.

The gas valve is DC powered but the hydraulic flow device is an interlock to prevent gas until there is a flow and if the boiler has not overheated and tripped the o/h switch then this may not be operating. The pin at the back must retract to allow gas to pass.

Tony

 

[ChrisR]

The pin at the back must retract to allow gas to pass.

You mean extend, I think.

 

[padsmith70]

Well, its working, tried some of the stuff from the thread....my system seemed to differ from what people were describing although symptoms exactly match....

Anyway, got a screw driver and turned the screw on the pump...seemed to have air coming out. So as I turned system on undid the screw and let air out. Took quite a few attempts, then suddenly the flamed kicked in for a few seconds...Became more frequent then stayed on.
Perhaps I didn't notice before, but now the BAR pressure goes higher to 2.5
The new radiator I changed doesn't seem to heat up or very slowly. Have bled it, checked both valves are open (TRV on one end)...it is upstairs and probably furthest away from the boiler .
This morning the flame went out for no reason. Played with dial that controls the heat/flame intensity (not sure what you call it) and it seemed to stay on longer. So watch this space I guess...But thank guys for pointers, I will update on any changes........

 

[padsmith70]

It seems the radiator with the TRV never get really hot. All the other rad's on the system (all old and I am replacing ) are amazing hot ...ANy idea