Hot water tank overflows

[Aidan]

Hi,
I would appreciate any help that anyone can give me with this problem. The hot water expansion tank throws out a lot of water particularly when I start up the heating system. There are 2 circulating pumps one at the boiler geound level and one at first floor level. I have tried reducing the pressure to 1 and 2 on each of these but this did not help. My plumber extended the expansion pipe to about height 2.5 feet above small expansion tank but this did nothing either. I have a dual temp regulated valve system in place that regulates the radiators downstairs and upstairs separately.

Any help appreciated to this problem

regards
Aidan

 

[bathjobby]

Has this just started happening ? if so whats changed ? what is the level of water in the f&e tanks before the overpumping begins ?

 

[Slugbabydotcom]

Please clarify if its pumping over through the vent or the tank is overflowing?

Whereabouts in your system do the feed and vent pipes connect into the rest of the pipework?

I am picturing a scenario that when both of your zone valves are closed for upstairs and down that the pump runing on the over-run stat is pulling down the feed and pumping over through the vent as the water has nowhere else to go.

If that rings true then best answer is to fit a de-aerator or at least to connect feed somewhere just below the vent connection. Opening a manual by-pass valve a little more if fitted will help to confirm if I am right and may provide a solution

 

[Aidan]

Has this just started happening ? if so whats changed ? what is the level of water in the f&e tanks before the overpumping begins ?

The system is 5 years old and this has been hapenning for the last 3 years but seems to be getting worse lately. The water level is right up to the level of the overflow outlet in the tank. I have tried lowering the water level in the tank but that did not seem to help.

 

[Aidan]

Please clarify if its pumping over through the vent or the tank is overflowing?

Whereabouts in your system do the feed and vent pipes connect into the rest of the pipework?

I am picturing a scenario that when both of your zone valves are closed for upstairs and down that the pump runing on the over-run stat is pulling down the feed and pumping over through the vent as the water has nowhere else to go.

If that rings true then best answer is to fit a de-aerator or at least to connect feed somewhere just below the vent connection. Opening a manual by-pass valve a little more if fitted will help to confirm if I am right and may provide a solution

its pumping over through the vent. I will check where the vent pipework connects into the system and revert back to you. Thanks - Aidan (apologies for my late reply)

 

[Aidan]

Please clarify if its pumping over through the vent or the tank is overflowing?

Whereabouts in your system do the feed and vent pipes connect into the rest of the pipework?

I am picturing a scenario that when both of your zone valves are closed for upstairs and down that the pump runing on the over-run stat is pulling down the feed and pumping over through the vent as the water has nowhere else to go.

If that rings true then best answer is to fit a de-aerator or at least to connect feed somewhere just below the vent connection. Opening a manual by-pass valve a little more if fitted will help to confirm if I am right and may provide a solution

its pumping over through the vent. I will check where the vent pipework connects into the system and revert back to you. Thanks - Aidan (apologies for my late reply)

The vent pipes are connected to the top of the cylinder and about 3/4 way up the side of the cylinder

 

[Slugbabydotcom]

Forget about the vent coming from the top of your cylinder as that is for HW and is not relevant

On the side of your cylinder there are two pipes one directly above the other.
These are the flow [top] and return [bottom]
The vent should come off the top of the flow pipe usually at the highest point as you have confirmed
The feed from your tank in the loft should connect in to your flow or return pipe somewhere.
It is the position of these two pipes [feed and vent] in relation to the pump that result in either pumping over or the opposite of your case which is sucking in through the vent.
Having these two pipes joining the system at the same place without the pump in between them will eliminate pumping over.

As a pump sucks and blows water around your system aka negative and positive pressure.
If the feed is on the negative side and the vent is on positive side the water will be forced out of the vent when the water can no longer flow around the system; because closed valves or other restrictions are preventing it.

A by-pass is a pipe running between the flow and the return and is often fitted after the pump. opening this valve if it is fitted gives the water somewhere easier to go rather than pumping over the vent.

I may have gone into too much detail there but I suppose thats better than not enough.

I will need a lot more info about your system to say more than I already have but there is possibly some fault there other than this, of which this is only a symptom and it may be beyond what can be achieved on here, however I suspect a control valve/system design fault, no or blocked by-pass, undersized vent pipe and a few less likely ones as well.

 

[Aidan]

Forget about the vent coming from the top of your cylinder as that is for HW and is not relevant

On the side of your cylinder there are two pipes one directly above the other.
These are the flow [top] and return [bottom]
The vent should come off the top of the flow pipe usually at the highest point as you have confirmed
The feed from your tank in the loft should connect in to your flow or return pipe somewhere.
It is the position of these two pipes [feed and vent] in relation to the pump that result in either pumping over or the opposite of your case which is sucking in through the vent.
Having these two pipes joining the system at the same place without the pump in between them will eliminate pumping over.

As a pump sucks and blows water around your system aka negative and positive pressure.
If the feed is on the negative side and the vent is on positive side the water will be forced out of the vent when the water can no longer flow around the system; because closed valves or other restrictions are preventing it.

A by-pass is a pipe running between the flow and the return and is often fitted after the pump. opening this valve if it is fitted gives the water somewhere easier to go rather than pumping over the vent.

I may have gone into too much detail there but I suppose thats better than not enough.

I will need a lot more info about your system to say more than I already have but there is possibly some fault there other than this, of which this is only a symptom and it may be beyond what can be achieved on here, however I suspect a control valve/system design fault, no or blocked by-pass, undersized vent pipe and a few less likely ones as well.

Hello Slugbabydotcom,
Thanks very much for your very detailed reply. It is much appreciated. I am having the installer of this system call round this week. I will gladly share this insight with him and hopefully together we can get resolution to the problem. I will indeed let you know what the remedy turned out to be.

Regards
Aidan

 

[Aidan]

Forget about the vent coming from the top of your cylinder as that is for HW and is not relevant

On the side of your cylinder there are two pipes one directly above the other.
These are the flow [top] and return [bottom]
The vent should come off the top of the flow pipe usually at the highest point as you have confirmed
The feed from your tank in the loft should connect in to your flow or return pipe somewhere.
It is the position of these two pipes [feed and vent] in relation to the pump that result in either pumping over or the opposite of your case which is sucking in through the vent.
Having these two pipes joining the system at the same place without the pump in between them will eliminate pumping over.

As a pump sucks and blows water around your system aka negative and positive pressure.
If the feed is on the negative side and the vent is on positive side the water will be forced out of the vent when the water can no longer flow around the system; because closed valves or other restrictions are preventing it.

A by-pass is a pipe running between the flow and the return and is often fitted after the pump. opening this valve if it is fitted gives the water somewhere easier to go rather than pumping over the vent.

I may have gone into too much detail there but I suppose thats better than not enough.

I will need a lot more info about your system to say more than I already have but there is possibly some fault there other than this, of which this is only a symptom and it may be beyond what can be achieved on here, however I suspect a control valve/system design fault, no or blocked by-pass, undersized vent pipe and a few less likely ones as well.

Hello Slugbabydotcom,
Thanks very much for your very detailed reply. It is much appreciated. I am having the installer of this system call round this week. I will gladly share this insight with him and hopefully together we can get resolution to the problem. I will indeed let you know what the remedy turned out to be.

Regards
Aidan

Hello Slugbabydotcom,
My plumber took a serious look at the design of the system and tried a test that has worked. He shut off the valve out of the small tank to stop water topping up the radiators. I have not seen any overflow through the expansion tank since this was tried. Now he plans to re-open the valve after inserting a non return valve at the required location. Does this make sense to you ?.

Regards
Aidan

 

[Slugbabydotcom]

Does this make sense to you ?.

Er no!! Without seeing your system I cant figure out where he would want to put this NRV for it to be of any use. I could see a by-pass valve being of use but the problem seems to me to be that the feed and vent pipes have the pump in between them. Adding an NRV to either of these pipes will cause problems. Fitting a de-aerator is the best way of curing it but failing that at least having the feed and vent connections on the same side of the pump and cllose together will suffice. If both of the pipes are under the same equal negative or positive pressure then pumping over will not occur

 

[Aidan]

Does this make sense to you ?.

Er no!! Without seeing your system I cant figure out where he would want to put this NRV for it to be of any use. I could see a by-pass valve being of use but the problem seems to me to be that the feed and vent pipes have the pump in between them. Adding an NRV to either of these pipes will cause problems. Fitting a de-aerator is the best way of curing it but failing that at least having the feed and vent connections on the same side of the pump and cllose together will suffice. If both of the pipes are under the same equal negative or positive pressure then pumping over will not occur

Thanks for your reply again. I have established that the excess water overflow is actually blowing up through the feed pipe. I established this by simply re opening the stop valve. A blow of water (about !/2 litre) entered the small tank through the feed pipe and not the vent pipe as I had previously thought. Do you still think that replacing this stop valve with a NRV can solve the problem without further repercussion.

regards
Aidan

 

[Slugbabydotcom]

Do you still think that replacing this stop valve with a NRV can solve the problem without further repercussion.

No

 

[Aidan]

Do you still think that replacing this stop valve with a NRV can solve the problem without further repercussion.

No

So, what are the further repercussion ???. I would like to know

 

[Slugbabydotcom]

A normal single or double check valve is unlikely to open to allow the low gravity pressure from the tank to enter the system these are normally used on mains or at least some forms of pumped flow. You risk the system runing dry in my opinion unless you are aware of a specific valve with this will not occur. Also a restriction such as an NRV in an unpumped part of the system provides a place where blockages can occur.

Hypothetically speaking
If it is as you say a stopvalve and not a gatevalve you have; as it should be then if this valve had a loose jumper and was fitted with the body at the top then this in itself would act as a non return valve as you are suggesting, It would also open under low pressure. The fact that this should be a gatevalve and not a stopvalve re-inforces what I am saying that non return valves have no place in a feed pipe.

Some boiler manufacturers permit a Single feed and vent pipe which would alleviate your problem at a stroke. Look in your boiler instructions to see if this is permitted. However whenever I have come across systems with a single feed and vent pipe I have always found the difficult to refill as air and water travelling in opposite directions in the same pipe is a bad policy.

If you want to do the job properly and in one go follow my previous postings about a de-aerator or fitting the feed and vent together

 

[Aidan]

A normal single or double check valve is unlikely to open to allow the low gravity pressure from the tank to enter the system these are normally used on mains or at least some forms of pumped flow. You risk the system runing dry in my opinion unless you are aware of a specific valve with this will not occur. Also a restriction such as an NRV in an unpumped part of the system provides a place where blockages can occur.

Hypothetically speaking
If it is as you say a stopvalve and not a gatevalve you have; as it should be then if this valve had a loose jumper and was fitted with the body at the top then this in itself would act as a non return valve as you are suggesting, It would also open under low pressure. The fact that this should be a gatevalve and not a stopvalve re-inforces what I am saying that non return valves have no place in a feed pipe.

Some boiler manufacturers permit a Single feed and vent pipe which would alleviate your problem at a stroke. Look in your boiler instructions to see if this is permitted. However whenever I have come across systems with a single feed and vent pipe I have always found the difficult to refill as air and water travelling in opposite directions in the same pipe is a bad policy.

If you want to do the job properly and in one go follow my previous postings about a de-aerator or fitting the feed and vent together

thanks, I will take your advice