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Hi, I’m having a problem with hw venting into the small header tank. This happens when it’s set to hw only or CH. I’ve tried lowering the water level in the header tank but it makes no difference. The incoming hot water is being taken back into system via the primary circuit 15mm supply so fortunately the level of water in the tank is remaining stable at whatever the level is set at. The system to all intents and purposes seems to be working, supplying HW and heating the radiators but it is unnerving having a tank of quite hot water sitting in the loft. My service engineer put MC3 Cleaner in the header tank about a week go but this has had no effect on the venting. Any helpful suggestions would be gratefully appreciated. Baz.
 
Was the circulating pump renewed recently, even if not make/model and present setting.
Thanks for replying, yes the pump was replaced about a year ago possibly a bit longer. When he came the service engineer said it was set at a too high a setting and turned it down, although it was his firm that installed it. However this has had no discernible affect on the venting. The pump is a Grunfoss UPS3 15-50/65 130. Baz.
 
Speed 1 at 4.6M will deliver 1m3/hr at 2.3M
Speed 2 at 5.4M will deliver 1m3/hr at 3.7M
Speed 3 at 5.8M will deliver 1m3/hr at 4.3M

Setting 1 shouldnt pump over but may not heat all rads
Setting 2 might pump over but should be finre for heating all the rads.
Setting 3 will definitely pump over.

Can you show/sketch your vent and cold feed arrangement, the popular method is to have the pump pumping from the boiler (flow) then the vent, then the cold feed, then the pump.
I have the best system of all, where the cold feed is teed into the vent adjacent to the F&E tank and will not pump over or pump back into the tank.
 

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Speed 1 at 4.6M will deliver 1m3/hr at 2.3M
Speed 2 at 5.4M will deliver 1m3/hr at 3.7M
Speed 3 at 5.8M will deliver 1m3/hr at 4.3M

Setting 1 shouldnt pump over but may not heat all rads
Setting 2 might pump over but should be finre for heating all the rads.
Setting 3 will definitely pump over.

Can you show/sketch your vent and cold feed arrangement, the popular method is to have the pump pumping from the boiler (flow) then the vent, then the cold feed, then the pump.
I have the best system of all, where the cold feed is teed into the vent adjacent to the F&E tank and will not pump over or pump back into the tank.
 
Ok thanks for that. I’ve attached a pic just taken, apologies for poor quality.
 

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There's some name for that contraption, the hot (flow) water from the boiler enters the top left side, the vent then goes straight up and over the F&E tank, the bottom right pipe goes to the pump suction and the cold feed comes straight down from the F&E tank. Its more than likely that this chamber is full of sludge etc and will have to be cut out, it can be renewed or just replaced with a "H", the vent and cold feed should be kept as close as possible.
 
There's some name for that contraption, the hot (flow) water from the boiler enters the top left side, the vent then goes straight up and over the F&E tank, the bottom right pipe goes to the pump suction and the cold feed comes straight down from the F&E tank. Its more than likely that this chamber is full of sludge etc and will have to be cut out, it can be renewed or just replaced with a "H", the vent and cold feed should be kept as close as possible.
 
I was looking at the wrong pump curves.
Even constant curve CC1 at 4.2M is quite high, as this acts like constant pressure on the UPS3, suggest trying it on constant pressure CP1 at 3M which may help with the pump over.

1668891421567.png
 
It’s a Tower air separator and is full of sludge.

The sludge is restricting flow and making it easier for the pump to pull water from the cold feed.

It then pumps it around the circuit and gets back to the air separator and the restriction, where it’s easier to pump up the vent and pull it back down the feed.

I’d replace the separator and renew the cold feed tee while you’re at it.
 
There's some name for that contraption, the hot (flow) water from the boiler enters the top left side, the vent then goes straight up and over the F&E tank, the bottom right pipe goes to the pump suction and the cold feed comes straight down from the F&E tank. Its more than likely that this chamber is full of sludge etc and will have to be cut out, it can be renewed or just replaced with a "H", the vent and cold feed should be kept as close as possible.
 
Thank you so much John and Timmy for your expert advice it is very gratefully received. I am sure armed with this information we will now be able to get this issue sorted. I will post again and let you know how it went. Baz.
 
Ensure you check out the pump setting before doing anything else especially if you had no pumpover with the old pump, lots of people had this problem after changing to the UPS3 as its a very powerful pump and its so called CC settings are not like the old pump settings, if you are not familar with setting it up, just post a close up photo of its LEDs, (obviously while running) and we can have a look.
 

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