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.

 

[RBG]

Slight edit to my previous post that you can have just one tank that covers both cylinder hot water and central heating with a primatic hotwater cylinder. Fairly rare (haven't been allowed to be fitted for years etc) and prob not relevant I just wanted to clarify my previous post.

 

[Trapper]

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.

Thanks, you have helped me get a better understanding now. Yes, the HW and CW taps ran dry and I guess that the HW cylinder got emptied.
I had forgotten that the CH system had a separate fill and expansion tank - this is the 4 gallon one.
Even though the CW and HW taps are back running as normal, I guess we will have to live with the inevitability of air locks in both should a drain down happen in future. Thankfully, that likely to be rare.

This leaves on remaining problem after the drain-down and that is the negative head pump that delivers HW to the loft bathroom. I am not getting any air or water coming out of either of the air-bleed valves as shown on the pics. I think the one on the left has a float valve that only lets out air but the other one is a simple thumb screw vent.

The pump shows "Fault" Does this mean that there is air trapped at the top of the cylinder? I have tried back filling via a mixer tap in the loft where the CW side is close to mains pressure. I would have thought the head of water above the cylinder ( from the 85 gallon tank above would be sufficient to fill the intake pipe for the pump. Being a centrifugal pump, the water should get past the impeller and fill both the intake and output sides of the pump and so give me something out of the bleed valve. Or am I missing something?

 

[Trapper]

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

Is it possible to get air locks even though the pipes are at a consistent downward gradient without any upward kinks where air could be trapped?

 

[RBG]

Thanks, you have helped me get a better understanding now. Yes, the HW and CW taps ran dry and I guess that the HW cylinder got emptied.
I had forgotten that the CH system had a separate fill and expansion tank - this is the 4 gallon one.
Even though the CW and HW taps are back running as normal, I guess we will have to live with the inevitability of air locks in both should a drain down happen in future. Thankfully, that likely to be rare.

This leaves on remaining problem after the drain-down and that is the negative head pump that delivers HW to the loft bathroom. I am not getting any air or water coming out of either of the air-bleed valves as shown on the pics. I think the one on the left has a float valve that only lets out air but the other one is a simple thumb screw vent.

The pump shows "Fault" Does this mean that there is air trapped at the top of the cylinder? I have tried back filling via a mixer tap in the loft where the CW side is close to mains pressure. I would have thought the head of water above the cylinder ( from the 85 gallon tank above would be sufficient to fill the intake pipe for the pump. Being a centrifugal pump, the water should get past the impeller and fill both the intake and output sides of the pump and so give me something out of the bleed valve. Or am I missing something?

What is the make / model of the loft pump? Does it get the hot feed from cylinder via an Essex flange on side of cylinder? I think it does from pic just want to confirm

 

[Trapper]

What is the make / model of the loft pump? Does it get the hot feed from cylinder via an Essex flange on side of cylinder? I think it does from pic just want to confirm

It's a Techflow (See attd) and yes the feed from the cylinder is via a flange on the side (see photo). There is "U" shaped loop before the pipe goes upwards to the pump intake

 

[RBG]

Thank you. I'm trying to find manual for it online but it appears to be a fairly old / discontinued pump.

If you are getting hot water to the taps around the house then it is unlikely to be an air block at the top of the cylinder. The essex flange on the side if far lower than the top.

 

[Alan Wright]

In my opinion you have a primatic cylinder which is temperamental, three cold water tanks when you should only have one cold water tank, and two huge power showers destroying your hot water cylinders thermocline. The system you have is over complicated.

I have put some notes below but I am not an expert on primatic cylinders and I do not want to be.
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You have a primatic cylinder, is also known as an indirect single-feed cylinder, which works by utilizing an air lock to separate the central heating water and domestic hot water within the cylinder. This air lock, typically a trapped bubble, prevents direct mixing of the two water types. The system uses a single header tank to feed both the heating circuit and the domestic hot water, and the trapped air bubble acts as a barrier.

Here are notes I found about your Primatic Tank.

Steps to Re-prime a Primatic Tank:

1. 1. Shut off the water supply:
   Turn off the main water supply to the property to prevent water from entering the tank while it's being drained and refilled.
   
   
2. 2. Drain the tank:
   Locate the drain valve on the Primatic tank and open it to drain the water. You may need to connect a hose to the drain valve to direct the water away from the tank.
   
   
3. 3. Refill the tank:
   Once the tank is drained, turn the main water supply back on. The tank will now start to fill with water, and the trapped air bubble will begin to form.
   
   
4. 4. Bleed the system:
   After the tank is full, you may need to bleed the system to remove any remaining air that might be trapped in the pipes or radiators. This involves opening bleed valves on the radiators and allowing any trapped air to escape.
   
   
   

 

[RBG]

Trapper. Are there any labels..etc indicating any information about the cylinder? name..model.etc

Is there a central heating pump?

 

[Trapper]

Trapper. Are there any labels..etc indicating any information about the cylinder? name..model.etc

Is there a central heating pump?

Sure, here is the tank label or what's left of it.

Yes there is Grundfos pump for the CH circulation

 

[Trapper]

Thank you. I'm trying to find manual for it online but it appears to be a fairly old / discontinued pump.

If you are getting hot water to the taps around the house then it is unlikely to be an air block at the top of the cylinder. The essex flange on the side if far lower than the top.

Yes, the pump is 20 years old but has seen very little use as the loft is only used by guests who are staying over. Techflow morphed into "New Team" and they went bust around 2006.

 

[Trapper]

In my opinion you have a primatic cylinder which is temperamental, three cold water tanks when you should only have one cold water tank, and two huge power showers destroying your hot water cylinders thermocline. The system you have is over complicated.

The Stuart Turner shower twin pump gives only a modest boost to the cold and hot water supply to the shower. It is mostly used only once per day by my wife. I prefer baths.
The other pump (Techflow) is single impeller and only used occasionally by guests up in the loft..

The "trapped bubble" in the primatic cylinder sounds intriguing and I will research that further.

 

[Trapper]

Further research shows that the cylinder was made by Baguley's Sons and all signs suggest that it is an indirect type.