Boiler not starting after drain down

[John.g]

Can you take a photo sometime of where the vent and cold feed are located, if you move back along the top of your pump you should see a sort of H, where coming from the boiler you should have vent, cold feed then pump suction (on the "top" in your case) the vent and cold feed should be within 150mm of each other.
With the pump running, have a look into the feed & expansion tank and look for any movement in the bottom of the tank or any sign of pump over through the vent.
If there is/was even the slightest restriction in the short section of piping between the vent and cold feed then this will lead to air ingress through the vent when the circ pump starts and stops and you can sometimes see this happening if you watch the vent while someone stops/starts the boiler, allow a few minutes for pump overrun when the boiler is stopped.
Another sign of long term pump over/back is a very dirty Feed & expansion tank.

 

[Rosscardwell]

Can you take a photo sometime of where the vent and cold feed are located, if you move back along the top of your pump you should see a sort of H, where coming from the boiler you should have vent, cold feed then pump suction (on the "top" in your case) the vent and cold feed should be within 150mm of each other.
With the pump running, have a look into the feed & expansion tank and look for any movement in the bottom of the tank or any sign of pump over through the vent.
If there is/was even the slightest restriction in the short section of piping between the vent and cold feed then this will lead to air ingress through the vent when the circ pump starts and stops and you can sometimes see this happening if you watch the vent while someone stops/starts the boiler, allow a few minutes for pump overrun when the boiler is stopped.
Another sign of long term pump over/back is a very dirty Feed & expansion tank.

 

[Rosscardwell]

Is this the point you mean?
The boiler is fully back to not working so I don’t think what the plumber did has fixed anything so that’s annoying. I never thought there was a problem the 3 way port as was working fine before I drained it.

I will have a look up in the loft tomorrow but I really think he missed the air lock Issue.

 

[John.g]

Yes I would think that H is the vent and cold feed.

Annoying all right but problem still the same.

Even if unlikely Its possible that a load of sludge has now lodged in the pump internals or/and the valve ports but hopefully not in the boiler Hx after that clean out even if thoroughly flushed down afterwards.

Did he replace the whole mid position valve, if so then he would have had to drain or partially drain down the system.??

Short of getting him back I would suggest isolating (switch out) the boiler, shut the pump isolating valves and loosen the pump (bottom) outlet pipe connection, re open the pump inlet valve fully and see can you vent any air, maybe do the same in reverse, I would probably remove the pump to inspect it for sludge build up but worth trying the above first?.