System sucking in air - suggested fix is convert to closed - looking for more info

[layperson12345]

Hi everyone,

I'm a newbie here, a layperson homeowner, stopping by in desperation to try and get a better understanding of my options regarding a diagnosis.

I have a conventional gravity heating system (cold water tank).

British Gas put in a new boiler and replaced most of the other bits (pump, condenser, flue) back in 2011.

The current boiler is a Worcester Greenstar 18Ri.

Over the last few years I have had nothing but problems. First the pump became really noisy. Then the boiler kept getting a flashing light and turning off.

I have had the same heating engineers working on it for at least three years and have had done everything they said needed doing. I must've spent at least £2000 so far.

I've had the boiler serviced every year, the pump replaced twice, a full power flush, new 3 way valve, several new rads, a magnaclean, new programmer and finally a new condenser.

And yet, still the blasted boiler keeps turning off with a flashing blue light.

Now the engineer is saying that the issue is that the system is sucking in air because the original pump was installed with "not enough head room". Apparently the newer pump is more powerful and is now causing the sucking in of air.

Every time it has happened I have to wait for them to come out and get rid of the air at £90 plus VAT per time. Plus we are without heating for the whole time which is a major issue as my mother is 72 and a cold will put her in hospital.

We were desperate the last time and Coronavirus had just started so we got another guy out cause he could come quicker. He said the same thing. He bled the system, turned the pump down, showed us how to reset the boiler and told us to see how that went. He said if having the pump set lower didn't solve the issue then the best choice was to convert the system to a closed system. At a cost of at least £500 not including VAT.

And then of course Coronavirus hit properly. It's happened again twice in two days and now I'm stuck.

I've googled converting an open system to a closed system but I can't find anything about it except for the more modern Megaflo type setups.

I'm hoping someone here can maybe explain a bit more about it...?

What does not enough head room even mean?

Is converting the system really the only thing that can be done?

What's involved in a conversion?

What are the implications of converting it with regards to maintenance and servicing etc?

Neither of the current engineers are able/willing to explain any of this in laymans terms.

I'm sick of throwing money at this problem. Then next time I do I want to be sure it's going to be the last time for a good long while.

Can anyone help me understand? Any help would be greatly appreciated. I've got a bunch of photos of the setup.

Thanks for reading my post.

 

[John.g]

I'm happy enough with my interpretation of it, At 95C the vapour (saturation) pressure is 8.63M BUT the atmospheric pressure alone is 10.34M and any pressure > the vapour pressure of 8.63M will stop the vapour forming, Even with zero static head the atmospheric pressure is giving a NPSA of (10.34-8.63) or 1.71M but Grundfos have a NPSR of 5M so a tank with its water level 3.3M above the pump CL must supply the remainder, (static head of 3.3M.)
so the NPSHA=NPSR?

 

[SJB060685]

NPSHR is minimum pressure required to avoid cavitation, so in essence equal to saturation pressure.

 

[John.g]

The Americans generally explain things in simple terms, try this very old explanation that I have had for years, It talks about NPSH, NPSHA and NPSHR.
The first few paragraphs explains it well, I think.

 

[SJB060685]

Link appears to be broken

 

[John.g]

Try this, back later.

 

[karltheplumber]

My first port of call would be to ensure there is enough height on the vent pipe for the header tank. I can't see the pipework properly in your pictures however it could be pumping over the vent.
This can cause all sorts of strange problems including air being dragged round the system and finding itself in the boiler causing lockout.
Also are the Flow and Return pipework in the correct orientation?

 

[John.g]

450mm is commonly given as the minimum height from the top of the vent to the F&E tank level.
There is a formula that uses (static height) the distance from the F&E tank level to the lowest point in the system, normally the boiler return. The calc is this height (in meters) X 40) + 150. If this static height is like my 2 storey house, 5 meters, then the calc is 5x40 + 150 or 350mm.

 

[doitmyself]

450mm is commonly given as the minimum height from the top of the vent to the F&E tank level.
There is a formula that uses (static height) the distance from the F&E tank level to the lowest point in the system, normally the boiler return. The calc is this height (in meters) X 40) + 150. If this static height is like my 2 storey house, 5 meters, then the calc is 5x40 + 150 or 350mm.

I have often wondered how the 450mm was calculated; but I don't see how the distance from tank level to the lowest point is relevant.

 

[John.g]

Yes, I've wondered a few times about it myself, the calculation part is also used I think for DHW cylinders except the measurement is taken from the bottom of the HWC but in either case the levels in the header tanks will only rise a few inches taking the expansion and in the event of cold water supply blockage will rise up the vent (open safety valve, or OSV) and overflow into the tank. You would need the vent sticking up through the roof to accommodate the expansion in either case without overflow. I can sort of understand the vent rising up 450MM or whatever in the vented boiler case as it possibly prevents the water overflowing when the circ pump starts/stops causing surging. The "X40" calculation might have some basis in the fact that water expands 4% at 100C?.

 

[SJB060685]

The vent must rise a minimum of 450mm above level in header tank on CH systems to prevent pressure surges from pump potentially pumping over as John says. I can't remember the calculation for HW cylinder requirements as its been ages since college. I will try to find in my text books though

 

[John.g]

Just thinking about the above (HW cylinder) again and the vent height. If you think of the system as a U tube with the cold leg consisting of the height from the CWST level to the (almost) bottom of the HWC and the hot leg as the distance from there back to the CWST level, then, especially when there is any demand for hot water, to keep the U tube balanced the height of (hot) water in the vent will be higher than the cold leg (to give equal heads) by 3X (4%X1000) mm or 3X40, 120mm @ 100C and 3X (1.83%X1000) mm or 3X18.3 mm, 55 mm @ 65C?? the extra height of 150mm may be added to prevent any air entering the hot water outlet pipe during very high draw off periods due to any syphoning effect.

 

[layperson12345]

Hi everyone,

I'm a newbie here, a layperson homeowner, stopping by in desperation to try and get a better understanding of my options regarding a diagnosis.

I have a conventional gravity heating system (cold water tank).

British Gas put in a new boiler and replaced most of the other bits (pump, condenser, flue) back in 2011.

The current boiler is a Worcester Greenstar 18Ri.

Over the last few years I have had nothing but problems. First the pump became really noisy. Then the boiler kept getting a flashing light and turning off.

I have had the same heating engineers working on it for at least three years and have had done everything they said needed doing. I must've spent at least £2000 so far.

I've had the boiler serviced every year, the pump replaced twice, a full power flush, new 3 way valve, several new rads, a magnaclean, new programmer and finally a new condenser.

And yet, still the blasted boiler keeps turning off with a flashing blue light.

Now the engineer is saying that the issue is that the system is sucking in air because the original pump was installed with "not enough head room". Apparently the newer pump is more powerful and is now causing the sucking in of air.

Every time it has happened I have to wait for them to come out and get rid of the air at £90 plus VAT per time. Plus we are without heating for the whole time which is a major issue as my mother is 72 and a cold will put her in hospital.

We were desperate the last time and Coronavirus had just started so we got another guy out cause he could come quicker. He said the same thing. He bled the system, turned the pump down, showed us how to reset the boiler and told us to see how that went. He said if having the pump set lower didn't solve the issue then the best choice was to convert the system to a closed system. At a cost of at least £500 not including VAT.

And then of course Coronavirus hit properly. It's happened again twice in two days and now I'm stuck.

I've googled converting an open system to a closed system but I can't find anything about it except for the more modern Megaflo type setups.

I'm hoping someone here can maybe explain a bit more about it...?

What does not enough head room even mean?

Is converting the system really the only thing that can be done?

What's involved in a conversion?

What are the implications of converting it with regards to maintenance and servicing etc?

Neither of the current engineers are able/willing to explain any of this in laymans terms.

I'm sick of throwing money at this problem. Then next time I do I want to be sure it's going to be the last time for a good long while.

Can anyone help me understand? Any help would be greatly appreciated. I've got a bunch of photos of the setup.

Thanks for reading my post.

A closed heating system just very basically speaking is the wee feed/expansion tank that is normally in loft to be removed and pipes to it capped off.
The system, (boiler type permitting), then requires a safety valve (pressure relief valve of usually 3bar) and an expansion vessel and a filling loop from mains water pipe connected to your heating system to top up pressure manually.
It shouldn’t be expensive to do, but your system must be sound, with no leaks or slight weeps including rad valves.
Remember a sealed heating system will be filled to and operate at a higher pressure to what it was, perhaps 3 or 4 times the pressure, so always a risk of dodgy work leaking, although hopefully all will be okay.
Do not be attempting this yourself as you could cause damage or leave system dangerous.
Your copper cylinder is a different water to your heating system and can remain untouched.

OK.

I hadn't noticed but this entire thread blew up with a technical discussion that is just waaaay over my head.

I don't know what to do now.

How do I know whether or not the system has been designed properly in the first place?

Or was it designed properly but now the new pump has ruined it?

How do I know what the proper solution is?

Converting the whole system when no-one else on my street has had to do so sounds wrong.

I have no idea what to do.

Thank you to everyone who posted though.

 

[SJB060685]

OK.

I hadn't noticed but this entire thread blew up with a technical discussion that is just waaaay over my head.

I don't know what to do now.

How do I know whether or not the system has been designed properly in the first place?

Or was it designed properly but now the new pump has ruined it?

How do I know what the proper solution is?

Converting the whole system when no-one else on my street has had to do so sounds wrong.

I have no idea what to do.

Thank you to everyone who posted though.

Hi.

Yes sorry, there's a few on here ie. John.g and myself that go a little overboard with the technical stuff, which can be confusing for homeowners.

Do you have a fault code with the flashing light on the boiler?

 

[John.g]

OK.

I hadn't noticed but this entire thread blew up with a technical discussion that is just waaaay over my head.

I don't know what to do now.

How do I know whether or not the system has been designed properly in the first place?

Or was it designed properly but now the new pump has ruined it?

How do I know what the proper solution is?

Converting the whole system when no-one else on my street has had to do so sounds wrong.

I have no idea what to do.

Thank you to everyone who posted though.

OK, I did suggest a few "cures" in post 6 but you might supply a few details of the pump first, don't know if you can post on here yet, if so, give a close up of the pump with the LEDs, if you cannot post, just give the make/model and which LEDs are illuminated on the left or on the right and we might be able to give a more appropriate setting.

When you have posted this go up to your attic/where ever and you will see a small tank of water which is the F&E (feed & expansion) tank, you will see a 22mm copper (vent) pipe rising up over this tank and then bending down like a walking stick, measure the distance from the tank water level to the top of the bend in this vent, then follow this and see where it is connected into the system.
You will also see a 15mm pipe coming out of the F&E tank bottom, this the cold feed make up, follow this and see where it is connected into the system.
If you can establish these points then it would be very helpful.
[automerge]1587999148[/automerge]
You can use the attached to see your present settings, I would suggest setting it to PP2 mode, ie: LED's: Green Yellow Blank Yellow Blank Blank.
[automerge]1587999399[/automerge]
Apoligies, PP2 should be
Green Yellow Blank Yellow Blank