Air in CH system and hot water returning to FE tank via the cold feed

[Tiggy1955]

I have a problem with air being sucked into my CH system creating airlocks in the radiators. The water is flowing back into the FE tank via the cold feed pipe. I can feel warm water coming through the feed pipe back into the tank as the tank water level slowly get higher. I can hear the overflow gurgling in the FE tank.

The system is 20 years old but the Worcester Bosch boiler is only 9 years old. All has worked perfectly well. I did have the classic blockage where the cold feed meets the hot return but the clogged pipes have been cut out and replaced.

I have fitted a new pump and it is set to the lowest speed. All of the radiators have been bled many times and balanced.

So the heating is working fine except that I have this problem of the air displacing the water back to the FE tank. The water it getting back into the tank a quite a rate - I would say about 2 litres per hour. This means that the rads need to be bled constantly.

Any ideas? Could it be an problem with the boiler itself?

 

[Ric2013]

First question: can you confirm that there is water in the F&E?

 

[Ric2013]

The water it getting back into the tank a quite a rate - I would say about 2 litres per hour. This means that the rads need to be bled constantly.

Can you re-word this please: not sure what you mean.

 

[Tiggy1955]

First question: can you confirm that there is water in the F&E?

Yes the tank is full. As the heating runs I can see the sediment being moved around the FE tank. I put my hand in the tank and you can feel warn water coming back in via the feed outlet.

 

[Tiggy1955]

Can you re-word this please: not sure what you mean.

The FE tank is fall as normal. However when the heating is running I can see the sediment at the bottom of the tank being moved around. I put my hand into the tank and can feel warm water coming back in via the cold outlet.

Because the tank is therefore getting fuller I scooped about 2 litres of it out. I turned the CH off. Bled all of the rads and did this again and about 30 mins later a further 2 litres had come back in. Is is not coming from the expansion pipe but I can hear that gurgling.

 

[Ric2013]

Hmm. So the water level continues to rise in the F&E even after the system is warmed up. And even if you continually bleed the radiators, the water rises in the F&E.

I assume you are taking water out of the F&E because there is no overflow?

 

[Tiggy1955]

Hmm. So the water level continues to rise in the F&E even after the system is warmed up. And even if you continually bleed the radiators, the water rises in the F&E.

I assume you are taking water out of the F&E because there is no overflow?

Yes the water is rising all the time. I have to bleed the rads every time the heating has been on. There is an overflow but I elected to scoop it our rather than let it get that full. In fact it was a pool of water outside that alerted me to the fact that water was returning to the FE tank.

 

[John.g]

I have a problem with air being sucked into my CH system creating airlocks in the radiators. The water is flowing back into the FE tank via the cold feed pipe. I can feel warm water coming through the feed pipe back into the tank as the tank water level slowly get higher. I can hear the overflow gurgling in the FE tank.

The system is 20 years old but the Worcester Bosch boiler is only 9 years old. All has worked perfectly well. I did have the classic blockage where the cold feed meets the hot return but the clogged pipes have been cut out and replaced.

I have fitted a new pump and it is set to the lowest speed. All of the radiators have been bled many times and balanced.

So the heating is working fine except that I have this problem of the air displacing the water back to the FE tank. The water it getting back into the tank a quite a rate - I would say about 2 litres per hour. This means that the rads need to be bled constantly.

Any ideas? Could it be an problem with the boiler itself?

Has this problem occured since the new pump fitting, if so you might post the make/model of the old pump and ditto for the new pump.

 

[Tiggy1955]

Has this problem occured since the new pump fitting, if so you might post the make/model of the old pump and ditto for the new pump.

No. It started before. I replaced the pump like for like (Grundfos UPS2). In actual fact I did't really need to replace the pump but did so at this time as a precaution because I know the last one that was fitted was a second hand one.

 

[John.g]

No. It started before. I replaced the pump like for like (Grundfos UPS2). In actual fact I did't really need to replace the pump but did so at this time as a precaution because I know the last one that was fitted was a second hand one.

The new pump will or should have PP (proportional pressure) control.
The present fixed speed setting 1 is equivalent to a 4M pump and for
most systems should not cause any pump over problems... however you could try setting it to one of the 3 PP settings which are all fairly close, I would suggest trying it on PP2 which will reduce the head considerably at the cost of reduced circulation through the system but might still be quite adequate for your purposes, if no pump over at this setting, I would suggest increasing it to PP3, if you still have pump over (at PP2) reduce it to PP1.

 

[Tiggy1955]

The new pump will or should have PP (proportional pressure) control.
The present fixed speed setting 1 is equivalent to a 4M pump and for
most systems should not cause any pump over problems... however you could try setting it to one of the 3 PP settings which are all fairly close, I would suggest trying it on PP2 which will reduce the head considerably at the cost of reduced circulation through the system but might still be quite adequate for your purposes, if no pump over at this setting, I would suggest increasing it to PP3, if you still have pump over (at PP2) reduce it to PP1.

The pump has 3 speed settings. Initially it was on 3 and I thought that was the problem so it is currently set to 1 and the problem still exists. I should mention we are in a bungalow so I think 1 is adequate anyway.

 

[Ric2013]

This doesn't sound like pump-over at all. And if the system is correctly designed, then the speed of the pump is immaterial.

I take it when you turn the boiler off and the system cools and you bleed the radiators, the F&E level is not dropping back down? You'd need to isolate the float valve aka ballcock to check as otherwise it will refill the F&E automatically.

I'm going to come up with the hypothesis that you have a hot water cylinder and that the coil in it is leaking. This would explain the water rising, though not sure where the air issue fits in. Do you have a cylinder or do you have a combi-boiler?

 

[John.g]

The pump has 3 speed settings. Initially it was on 3 and I thought that was the problem so it is currently set to 1 and the problem still exists. I should mention we are in a bungalow so I think 1 is adequate anyway.

Agreed, speed setting 1 should be fine in normal circumstances but by selecting PP control it will reduce the head from say 3M to ~ 1.5/1.7M and IF the F&E tank "movement" dies down or ceases then at least it will tell you something.

 

[Tiggy1955]

This doesn't sound like pump-over at all. And if the system is correctly designed, then the speed of the pump is immaterial.

I take it when you turn the boiler off and the system cools and you bleed the radiators, the F&E level is not dropping back down? You'd need to isolate the float valve aka ballcock to check as otherwise it will refill the F&E automatically.

I'm going to come up with the hypothesis that you have a hot water cylinder and that the coil in it is leaking. This would explain the water rising, though not sure where the air issue fits in. Do you have a cylinder or do you have a combi-boiler?

When I bleed the rads the FE level does drop and water enters via the ballcock. Yes we have a hot water cylinder.

 

[Ric2013]

So if your ballcock were not refilling the F&E, and no overflowing took place, you think the volume of water in the system would stay the same? There isn't any being added, by, say, a leak from the coil in your hot water cylinder?

 

[Tiggy1955]

Agreed, speed setting 1 should be fine in normal circumstances but by selecting PP control it will reduce the head from say 3M to ~ 1.5/1.7M and IF the F&E tank "movement" dies down or ceases then at least it will tell you something.

How do I change the PP setting? The pump only has the 3 setting selected via a button.

 

[Tiggy1955]

This doesn't sound like pump-over at all. And if the system is correctly designed, then the speed of the pump is immaterial.

I take it when you turn the boiler off and the system cools and you bleed the radiators, the F&E level is not dropping back down? You'd need to isolate the float valve aka ballcock to check as otherwise it will refill the F&E automatically.

I'm going to come up with the hypothesis that you have a hot water cylinder and that the coil in it is leaking. This would explain the water rising, though not sure where the air issue fits in. Do you have a cylinder or do you have a combi-boiler?

I thought I would post this photo of the piping as it might help to explain the problem in more detail? This piping is directly above the boiler.

 

[Tiggy1955]

So if your ballcock were not refilling the F&E, and no overflowing took place, you think the volume of water in the system would stay the same? There isn't any being added, by, say, a leak from the coil in your hot water cylinder?

How could I check that please?

 

[John.g]

How do I change the PP setting? The pump only has the 3 setting selected via a button.

It has 3 fixed speed settings and 3 PP settings, you press and hold the button for 5 secs to change from FP to PP (page 7 of attachment).
"When you press the button for five seconds, the pump
will change from fixed-speed operation to proportional pressure
control"

 

[Ric2013]

How could I check that please?

If you were to isolate the ballcock and let the system cool, bleed the air out and add back the water you have scooped out, then you should have the same level you started with.

Looking at your photo, I am wondering where your vent is? I am assuming there isn't one? If so, then the system isn't pumping over.

Assuming your pump is somewhere on the boiler flow then anything between the cold feed and the pump inlet is running at a vacuum when the pump is on and there could be a minor weep which is admitting air to the system. Could be a radiator valve, the pump inlet gate valve stem, the pump inlet washer, or one of the joints in or near the boiler.

Alternatively, if there was a blockage, then there must be some degree of scale or rust in the system. Could be the boiler is kettling and creating steam, but I wouldn't imagine that steam could continue to survive as such for very long in the sort of quantity you are experiencing.

You seem to enjoy problem solving, so hopefully this will give you some ideas, but I am beginning to think you may need a professional to attend and have a good look at the system and how it is all arranged.

 

[sammathias]

If the coil has failed in the cylinder the small feed and EXPANSION tank would constantly be overflowing due to the hot water cistern being higher/bigger. It's normal for the water to rise slighlts in the f+e. After all where else is the expanded water going to go????

 

[Tiggy1955]

If you were to isolate the ballcock and let the system cool, bleed the air out and add back the water you have scooped out, then you should have the same level you started with.

Looking at your photo, I am wondering where your vent is? I am assuming there isn't one? If so, then the system isn't pumping over.

Assuming your pump is somewhere on the boiler flow then anything between the cold feed and the pump inlet is running at a vacuum when the pump is on and there could be a minor weep which is admitting air to the system. Could be a radiator valve, the pump inlet gate valve stem, the pump inlet washer, or one of the joints in or near the boiler.

Alternatively, if there was a blockage, then there must be some degree of scale or rust in the system. Could be the boiler is kettling and creating steam, but I wouldn't imagine that steam could continue to survive as such for very long in the sort of quantity you are experiencing.

You seem to enjoy problem solving, so hopefully this will give you some ideas, but I am beginning to think you may need a professional to attend and have a good look at the system and how it is all arranged.

Hi Ric2013 - Thanks for all the info so far. To answer some of your points:

The vent (and by that I assume you mean the pipe that dangles over the FE tank?) is T’d into the boiler flow and is plastered into the wall about 20” to the right of the cold feed shown in the photo.


The pump is in the airing cupboard and I assume is attached to the boiler flow (pretty sure it is - the pipes come up through the floor boards). Above the pump is the 3 way motorised valve - which appears to be functioning correctly when you switch between CH and HW.


As for enjoying solving problems - yes I do - but this one is driving me nuts!!!

Thanks again.

 

[Ric2013]

Ah, so your arrangement is something like this then?

If so, the pump is pulling on the vent and could be pulling in air if it runs too fast. Unfortunately, in PP mode, the pump will start fast even when it then slows down. What you have there is probably a residual of an old legacy system much more than 20 years old that worked very well with the old boilers that had negligable resistance to flow, not so well with a modern boiler. Possibly has never been fully modernised. The pump may well have been on the return once upon a time.

You can try setting down the pump as other have suggested, but my feeling is that this kind of setup is prone to this sort of problem and you might want to look at getting the system reconfigured.

One important question: Did it used to work okay and when did this change?

View attachment 36394

 

[John.g]

Ah, so your arrangement is something like this then?View attachment 36395

If so, the pump is pulling on the vent and could be pulling in air if it runs too fast. Unfortunately, in PP mode, the pump will start fast even when it then slows down. What you have there is probably a residual of an old legacy system much more than 20 years old that worked very well with the old boilers that had negligable resistance to flow, not so well with a modern boiler. Possibly has never been fully modernised. The pump may well have been on the return once upon a time.

You can try setting down the pump as other have suggested, but my feeling is that this kind of setup is prone to this sort of problem and you might want to look at getting the system reconfigured.

One important question: Did it used to work okay and when did this change?

View attachment 36394

My own system has a combined vent and cold feed, ie the cold feed is teed directly into the vent where it passes by the Feed & Expansion tank, I know of a number of systems like Tiggy1995,s above that were modified to this combined system, this obviously isn't allowed in a solid fuel system. However he did say his system worked well as is and the boiler was renewed 9 years ago, I don't think he has had this problem for the past 9 years.

Re the pump speeding up on PP setting, it does, but only for a few seconds to find its steady state condition, its only the press of a button to try it out and it may alleviate if not cure the problem until a permanent solution is found.

 

[Tiggy1955]

Ah, so your arrangement is something like this then?View attachment 36395

If so, the pump is pulling on the vent and could be pulling in air if it runs too fast. Unfortunately, in PP mode, the pump will start fast even when it then slows down. What you have there is probably a residual of an old legacy system much more than 20 years old that worked very well with the old boilers that had negligable resistance to flow, not so well with a modern boiler. Possibly has never been fully modernised. The pump may well have been on the return once upon a time.

You can try setting down the pump as other have suggested, but my feeling is that this kind of setup is prone to this sort of problem and you might want to look at getting the system reconfigured.

One important question: Did it used to work okay and when did this change?

View attachment 36394

Yes that diagram is correct. The system has never been reconfigured. We have lived here since the house was built. The only thing that has changed is the boiler. The original was an Ideal now a Worcester Bosch (I think the builder might have used BG to install the heating system at the time - over 20 years actually).

You are also correct in that this problem has just started in the last few weeks. I have also just realised something else this evening. When the system is set to CH and HW the heating hardly gets hot. On CH only it heats up nicely. I'm at the end of what I think I can do so I'm going to get a heating engineer to have a look at it now. I'm even considering replacing the whole lot with a combo boiler. We live in a bungalow and there are only two of us so a combo should be OK. I'll get advice.