Boiler Won't Run After Drain Down

[OscarFoxtrot]

Hello.

Did a partial drain down on my parents heating system this morning in order to remove a radiator and fit valves on the pipe work below the floor ahead of a bathroom refit (with new rad).

Fitted a bung in the header tank and closed all other rads but still ended up taking a bit of water out the system.

Slowly removed bung, opened new valves to bleed pipe work, then opened all rads and switched on boiler and controls for heating and HW

Boiler will fire, run for a minute or two then stop and sit "ready"

Boiler is a Buderus 800-29

Any ideas?

Cheers

 

[footprints]

Sorry posted in error, deleted.

 

[Hugh Jaleak]

Still air in the system by sound of it.

 

[OscarFoxtrot]

Was thinking that but not sure how to test/sort.

The automatic air vent whistled away a few times, I tried bleeding the pump and also opened the drain cock outside for a bit and the water flowed through

 

[OscarFoxtrot]

Just tried a mains pressure hose on the drain cock and opened it. Nothing came through the open vent at the header tank like I thought it would.

Stumped with this one.

 

[easyflow]

Would come through the outlet of header tank, but your looking at airlock.
All rad valves open ?

 

[footprints]

When you drained off at the drain cock outside, did the tank start to fill? If not blocked down feed.

 

[OscarFoxtrot]

Thanks guys.

Tried it with all rad valves open and also with all closed. Drained a bit off the header tank and held the ball up to see if it filled from outlet when pressured from mains outside but no joy. It's quite a height (5m or so) from header tank to draincock but mains pressure would still win?

Yes, tank is filling when drain cock is open.

 

[OscarFoxtrot]

Also, in the short time the boiler is fired up it seems able to heat the HW cylinder before shutting off.

 

[stardanny]

Airlock in return pipework. Have you got any AAV or air bleed valve in airing cupboard?

Do keep going with hot water from boiler to cylinder, in time it will clear, once that going ok, do the heating on it own.

Daniel.

 

[footprints]

OK so if the ball cock runs when the drain is opened chances are the cold feed is all right.

Do you have motorised valved did you set them to manual open position when filling?

Is the pump running, try a screwdriver on the body and put your ear to the handle end as a stethoscope.

Look for air vents at high level where the pipe drops.

Otherwise even for old codgers like me who have a few decades of experience we can spend hours sorting air locks!

As said does the boiler reset or remain locked out?

 

[holty]

sometimes best just left overnight etc. had one were i tried all sorts. spent hours and managed to get most rads working except 2 rads downstairs on drops with drain offs. left overnight they worked fine. ps check for a gate valve on the hw return off the cylinder or a manual bypass. a manual bypass can cause a few problems. ps f&e would overflow before it came out of the vent, whilst back feeding. unless you bung the feed.

 

[OscarFoxtrot]

Many thanks for the suggestions.

Gave up for the night just before 6. Will have another go tomorrow. The have a woodburning stove for heat too so its not all bad.

Couldn't see any air vents or bleed valves other than the one on the boiler itself.

Pump was spinning. I opened the screw to bleed it and some water came out but it wasn't much and looking inside the pump there only seemed a small amount sitting in the bottom of the pump. Is that normal? Not sure why but I expected a bit more water to come out with a bit more pressure.

Motorised valve is by the boiler and was set to manual although I was later told its been troublesome in the past.

When I was backfeeding I had the mains pressure on the open drain for a minute or two but nothing happened at the tank.

 

[holty]

back feeding on a drain off you might have closed the washer . or just give it more time. can take longer than you think

 

[OscarFoxtrot]

Thanks Holty. If I can't figure it out I'll give the back feeding another go. Just gets a bit nerve-wracking filling all that water into the system and not seeing anything happening!

If all else fails I'll just phone someone who knows what they're doing