Help! Before I rip up the floor boards

[Trapper]

First post so please bear with me.

Some years ago, we had a loft conversion done. In the loft were two 85 gallon cold water tanks - one supplying the hot water system and one the cold taps etc. Our CH is an open vented system. These were relocated in a different position in the loft and then boxed in. And for whatever reason a new small header tank (about 4 gallons) with a ball cock was added.

Early after the conversion, we experienced an air lock in both the HW and CW taps but we rectified this by attaching a hose at mains pressure and force back-filling through the cold and hot taps.

The air locks re-emerged again last week after we had to drain the system to replace a radiator.

This tells me there is an air-lock somewhere and I have crawled in to the boxed in area where the tanks are ( not easy when one is 79!) . I found one supply pipe (from the HW tank) that had a marginal sag in it before it disappeared into a hole in a joist. I lifted that to give a proper gradient. Time will tell if this will help.
To follow the pipes after they disappear through the joists will mean lifting carpet and floorboards after re-positioning one of the tanks.

Can someone explain why the third small header tanks is there?

 

[ShaunCorbs]

Air locks are common practice on heating / domestic hot and cold water system

Where is the air lock / what’s not heating

 

[Trapper]

Air locks are common practice on heating / domestic hot and cold water system

Where is the air lock / what’s not heating

Could not get water out of any hot or cold taps following a drain down. Both cold water tanks in the loft were emptied and I guess that's when air got in to the outgoing pipes from both tanks.
After reconnecting mains supply and filling the tanks both hot and cold taps did not supply water.

I then back-filled the HW and CW taps pipes using a hose at mains pressure. After that they worked OK. But then I had a problem with a negative head single impellor pump that supplies HW to the loft bathroom.

You say airlocks are common but if there is a constant downhill gradient on the pipes from the loft tanks then that should not happen- surely? Similarly , if back filling from below clears the airlock, then doesn't that suggest there is a sag somewhere in the pipe run?

Now going back to my original question..... why do I end up with 3 loft tanks instead of 2 after the loft conversion?

 

[ShaunCorbs]

Could not get water out of any hot or cold taps following a drain down. Both cold water tanks in the loft were emptied and I guess that's when air got in to the outgoing pipes from both tanks.
After reconnecting mains supply and filling the tanks both hot and cold taps did not supply water.

I then back-filled the HW and CW taps pipes using a hose at mains pressure. After that they worked OK. But then I had a problem with a negative head single impellor pump that supplies HW to the loft bathroom.

You say airlocks are common but if there is a constant downhill gradient on the pipes from the loft tanks then that should not happen- surely? Similarly , if back filling from below clears the airlock, then doesn't that suggest there is a sag somewhere in the pipe run?

Now going back to my original question..... why do I end up with 3 loft tanks instead of 2 after the loft conversion?

But that doesn’t explain how the hot and cold tanks were drained via the heating eg via replacing / draining a radiator ?

 

[Trapper]

But that doesn’t explain how the hot and cold tanks were drained via the heating eg via replacing / draining a radiator ?

We did not re-open the mains supply to the loft tanks promptly so they both emptied before we remembered.

 

[RBG]

We did not re-open the mains supply to the loft tanks promptly so they both emptied before we remembered.

So what you are saying is that the tanks supplying hot (via cylinder) and cold water to taps drained down via the central heating. In that they are connected to the central heating system

The smaller header tank would be the fill and expansion for the central heating system. The larger tanks should be solely for the hot and cold water to taps.