Automatic Bypass Valve Query

Tigermad · Jan 13, 2019

I had an automatic bypass valve fitted to my unvented system yesterday and it was left at 0.4. Goes from 0.1-0.5. Anyhow I thought I would set it today according to the instructions. So I closed it off completely to th 0.5 mark and then turned all the trvs on. I then began turning it until the pipe started to get warm. Problem is the abv is in the airing cupboard and it is fitted to the pipes marked flow and return. The flow pipe is hot but the return pipe remains stone cold. Even after leaving the heating on for 10 minutes. So turning the valve makes no difference. Am I doing something wrong? Why is the return pipe stone cold?
I just tried turning the heating off and the pipe from the ABV got red hot even though the ABV is turned off

Ignore the non copper pipes. These are from the old system and are redundant.

Aire · Jan 13, 2019

I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Is the abv fitted before or after the zone valve?

Tigermad · Jan 13, 2019

Craig Watson said:
I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Do you mean the horizontal one? The horizontal one is coming downhill from the flow to return. Is this wrong? The return is on the left of the bypass and the flow is on the top (horizontal), the one with the arrow. The zone valve is attached to the return.
The unvented hot water cylinder is in the loft so the abv is before the zone valve from the boiler but after the zone valve coming down from the cylinder.

SimonG · Jan 13, 2019

Craig Watson said:
I presume the pipe to the zone valve is the flow? If it is then the abv looks to fitted the wrong way.

Is the abv fitted before or after the zone valve?

Glad it wasn't just me. Thought I'd had too much beer last night.

Tigermad · Jan 13, 2019

So is it right or wrong after my reply?

Aire · Jan 13, 2019

Sounds like it's fitted ok, unless the valve is faulty or blocked then you shouldn't have any issues setting it up.

Tigermad · Jan 13, 2019

So which pipe do I have to feel getting warmer. The very small piece on the left going to the return?

John.g · Jan 13, 2019

Tigermad said:
I had an automatic bypass valve fitted to my unvented system yesterday and it was left at 0.4. Goes from 0.1-0.5. Anyhow I thought I would set it today according to the instructions. So I closed it off completely to th 0.5 mark and then turned all the trvs on. I then began turning it until the pipe started to get warm. Problem is the abv is in the airing cupboard and it is fitted to the pipes marked flow and return. The flow pipe is hot but the return pipe remains stone cold. Even after leaving the heating on for 10 minutes. So turning the valve makes no difference. Am I doing something wrong? Why is the return pipe stone cold?
I just tried turning the heating off and the pipe from the ABV got red hot even though the ABV is turned off

Ignore the non copper pipes. These are from the old system and are redundant.

View attachment 36343
View attachment 36344

The 0.1 to 0.5 settings are 0.1 bar to 0.5 bar or 1 M (meter) to 5 m.
The purpose of the ABV is to to maintain a minimum flow rate through the boiler on pump over run and also to maintain a minimum flow rate in the event of a very low heat demand where some/all of the TRVs are throttled in.
I presume that you were just testing its functionality with the above test with all TRVs ON (open??) and a setting of 1 M (0.1). Now the circ pump, depending on its speed setting may or may not be producing 1 M head with a large flow rate (all TRVs open) so you may not have got any flow rate due to this (pump head < 1 M) and maybe a circ pump speed setting of only 1?.
You could look at the pump make/model & current speed setting, then assuming that you need say 0.3 M3 per hour flowrate, by looking at the pump speed curves you can see what pump head is required, for example if the speed setting is 2 then the pump head at this speed required might be 3M so you would set the ABV to 0.3, and so on, you can then test it by shutting off the TRVs and ensure it is then opening.

John.g · Jan 13, 2019

Here is a example of one ABV setting.

Tigermad · Feb 11, 2019

Hi folks me again. Something is not right since the bypass has been fitted. Nearly every night at 6.40pm there a crackling /gushing water sound through the lounge radiator valve. This rad is nearest to the boiler. I have the hot water cylinder programmed on my evohome system to turn off at 6.40pm so I think it’s linked to this. Any ideas why this is happening?

Harvest Fields · Feb 11, 2019

Air? Valve not quite open enough?

Chuck · Feb 11, 2019

Tigermad said:
Hi folks me again. Something is not right since the bypass has been fitted. Nearly every night at 6.40pm there a crackling /gushing water sound through the lounge radiator valve. This rad is nearest to the boiler. I have the hot water cylinder programmed on my evohome system to turn off at 6.40pm so I think it’s linked to this. Any ideas why this is happening?

At 1839 the boiler is blasting away and the pump is pumping lots of hot water around the DHW loop though the cylinder.

At 1840 and 0 seconds the HW zone valve slams shut but the pump and boiler don't instantly respond so the water flows (fast) round the path of least resistance, which is either the radiator circuit or the ABV depending on how it is set.

By 1840 and 30 seconds the boiler power has been cut back and the pump has adapted to the new conditions and order is restored again.

The problem with ABVs is that they detect and act on pressure differences, which are only indirectly related to the flow rate in a system with TRV's and/or a smart pump. ABVs work pretty well with 'dumb' (constant displacement rate) pumps but not so well with 'smart' (constant pressure) pumps.

To further complicate the story, the purpose of an external ABV has changed over the years. Originally it was an energy-saving refinement to a traditional 'bypass radiator' that was always on ensure a minimum flow rate through the boiler. These days this is not usually needed but ABVs are often still used to to ensure that there is sufficient heat capacity in the circulating circulating water to avoid heat-stress damaging the heat exchanger. Some boilers, typically ones with robust stainless steel heat exchangers don't require an external ABV. Others, particularly ones with aluminium heat exchangers and low water volumes, require not just an ABV but also a minimum loop volume connecting it to the boiler.

As always, the installer needs to read the manufacturer's installation instructions carefully and follow them to the letter.

Tigermad · Feb 11, 2019

Chuck said:
At 1839 the boiler is blasting away and the pump is pumping lots of hot water around the DHW loop though the cylinder.
At 1840 and 0 seconds the HW zone valve slams shut but the pump and boiler don't instantly respond so the water flows (fast) round the path of least resistance, which is either the radiator circuit or the ABV depending on how it is set.

The problem with ABVs is that they detect and act on pressure differences which are only indirectly related to the flow rate. They work pretty well with 'dumb' (constant displacement rate) pumps but not so well with 'smart' (constant pressure) pumps.

To further complicate the story, the purpose of an external ABV has changed over the years. Originally it was to ensure a minimum flow rate throuh the boiler but these days it is often to to ensure that there is sufficient heat capacity in the circulating circulating water to avoid heat-stress damaging the heat exchanger. Some boilers, typically ones with robust stainless steel heat exchangers don't require an external ABV. Others, particularly ones with aluminium heat exchangers and low water volumes, require not just an ABV but also a minimum loop volume connecting it to the boiler.

As always, the installer needs to read the manufacturer's installation instructions carefully and follow them to the letter.

Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

Tigermad · Feb 11, 2019

Harvest Fields said:
Air? Valve not quite open enough?

No air in the system because I have tried to bleed all rads a few times now. Although the towel rail upstairs needs constant bleeding and i guess it’s the last rad on the circuit and something weird happens with it. But this thing with the towel rail was happening before the bypass was fitted.

Do you mean the valve on the rad or bypass? The noise is mainly on the left hand side of the radiator as the water goes in.

John.g · Feb 11, 2019

Tigermad said:
Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

You disable it by fully closing it, did you ever establish if it is in fact fitted correctly by opening it fully while the boiler is firing normally, you should then feel both flow and return pipes very hot.

Harvest Fields · Feb 11, 2019

Yes on the rad, also you may have mentioned this already but what setting is the pump on?

Tigermad · Feb 11, 2019

John.g said:
You disable it by fully closing it, did you ever establish if it is in fact fitted correctly by opening it fully while the boiler is firing normally, you should then feel both flow and return pipes very hot.

Yes. The pipes eventually got hot. Think I was doing something wrong when checking it. So if I completely close it I can see if the noise gets better without it?

Tigermad · Feb 11, 2019

Harvest Fields said:
Yes on the rad, also you may have mentioned this already but what setting is the pump on?

I have tried opening the lock shield valve a bit and closing it but made no difference whilst the noise was happening. The pump is built in to the boiler and it can run on either 70 percent or 100 percent. It’s on the default of 70 percent.

Chuck · Feb 11, 2019

Tigermad said:
Thanks. The radiator noise was better before the bypass was fitted. Can I disable it by fully opening it?

No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

Tigermad · Feb 11, 2019

Chuck said:
No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

Thanks. Sorry I meant fully close it to disable it completely.

John.g · Feb 11, 2019

Chuck said:
No. Don't "fully open" it. It should be set to operate at the highest pressure difference that allows it to achieve its intended purpose.

If you are determined to play around open it by small amounts, say quarter turns until it reduces the 1840 noise. But, if you open it enough to completely eliminate the 1840 noise you'll probably have gone too far and have replaced one problem with another.

Fully opening it was simply to establish if it was/is plumbed in properly.

John.g · Feb 11, 2019

Tigermad said:
I have tried opening the lock shield valve a bit and closing it but made no difference whilst the noise was happening. The pump is built in to the boiler and it can run on either 70 percent or 100 percent. It’s on the default of 70 percent.

Any idea what make/model of circ pump fitted.?

Tigermad · Feb 11, 2019

John.g said:
Any idea what make/model of circ pump fitted.?

Hi. It’s inside an Ideal Vogue S32 gen boiler.

John.g · Feb 11, 2019

Tigermad said:
Hi. It’s inside an Ideal Vogue S32 gen boiler.

Thanks, could you post the setting up instructions of your ABV, it should then be relatively easy to set it up properly.

Tigermad · Feb 11, 2019

John.g said:
Thanks, could you post the setting up instructions of your ABV, it should then be relatively easy to set it up properly.

Here you go. Thanks

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