Vaillant 837 Ecotec. Gas Inlet Pressure Problems

I've had some issues with inlet pressure and have gone through a steep learning curve to understand what pressures are required at the boiler. I'm no engineer, but I have used this site to understand more about the requirements before I undertook expensive and inconvenient work.

I have a Vaillant 837 Ecotec and when recently serviced the gas inlet pressure (when on full demand) was 12.5Mb. The service engineer put this down to the pipe size being only 22mm, whereas he felt it should be 28mm. However he did also note the pressure at the meter (when the boiler was on full demand) was only registering 17mb.

This service engineer was not the same company that did the original installation, but when I spoke to the original engineer about this he indicated that when the boiler was commissioned it was fine. In fact he said that the previous boiler, which was situated about 4 feet away from the new one had old 18mm pipework and that was OK. He was right and I checked the service report on this and it was showing 17.5mb (on full demand). He suggested I get the gas pressure looked at coming into the meter before any work was undertaken.

That made me slightly suspicious of the new engineer's motives as he initially seemed reluctant that I get someone to look at the pressure at the meter. He even suggested that I should get the pipework changed first and then if there was still a problem I should call in National Grid! I'm no rocket scientist, but I'm also not stupid and know when I'm being spun a yarn!

I therefore used this site to increase my knowledge of gas pressures and discovered that National Grid are obliged (FOC) to ensure that pressure at the meter should be between 19 and 23mb (boiler on full demand). I therefore called them out before I undertook any remedial work on my pipework and they cleared a blockage and changed the gas governor.

The pressure at the meter is now 22mb (boiler on full demand) and the reading at the boiler is 18Mb - I know I've measured it myself (I know I shouldn't but it seemed the only way to satisfy myself). Although the 4mb drop from meter to boiler is a little above what an ideal installation would be, it's acceptable for the Vaillant 837 boiler, which should read between 17mb and 25mb when on full demand.

What I have learned from this is that my service engineer was far too quick to assume that the pipework from meter to boiler was defective. National Grid are more than willing to come out and look at things and makes some tweeks and this costs absolutely nothing at all.

In fact I also learned that the gas pressure at the meter varies during the time of the day and the weather. The colder the weather the more people that are using their boilers and the lower the pressure at the meter. Er go, the lower the pressure at the boiler.

Having said that, if I knew that 28mm pipework was standard when the central heating system was being installed then I would have said something, but you do rely upon the knowledge of the engineer and his experience.

I hope this helps someone else in a similar position. If I have got any of these facts wrong then I'm more than happy to be told so by a registered CORGI engineer.

A.

Hi A.

It's not uncommon for an 837 ecoTec to need some part of the installation pipework run in 28mm. After all it is a 37kW boiler.

The pressure checks should also include checking when all of your gas appliances are on at the same time.

There are gas pipework size calculations that can be made to establish the correct size for an installation.

Andy.

I dont really know why you are writing all this. You are not apparently asking any technical questions.

Most people have a competent engineer to install their boiler and take his advice.

You seemed to have someone who was rather less competent and possibly trying to get you to spend money with him.

I have no idea who he was or if he is an employee or a sole trader. If an employee then you should make a written complaint to his boss and for either perhaps to CORGI as well as he was demonstrating a lack of competence.

The message is simple, call someone else in future.

Tony

If the working pressure at the meter is 22mb, and the inlet pressure at the appliance is 18mb there is a problem with the installation pipework. The manufacturer may accept a lower inlet pressure, but our regs dont. There should be no more than a 1mb drop between the meter and appliance when in operation. This is most commonly down to pipework being undersized.

Thanks very much for your reply Agile. You're right I'm not asking a direct question, but I wanted to post this to help anyone else out in a similar situation. I hadn't realised that this site is purely there to ask technical questions. All I wanted to do was pass on my knowledge and story to anyone else who may be in a similar position.

Andy has been kind enough to suggest that the tests should be made when all gas appliances are turned on. Thank you, I've done this and I measure 16Mb at the boiler when the cooker (5 rings) is turned on.

Interestingly enough that wasn't a test that my servicing engineer made!

I'd rather not have to pay £500 and rip up floorboards to change the complete run of pipework for 1mb pressure. There is a 3 metre run in the garage where the 28mm pipework could be changed without great costs or incovenience? In your expert opinion, do you think this would help?

Thanks again.

A.

boabcelt said:

If the working pressure at the meter is 22mb, and the inlet pressure at the appliance is 18mb there is a problem with the installation pipework. The manufacturer may accept a lower inlet pressure, but our regs dont. There should be no more than a 1mb drop between the meter and appliance when in operation. This is most commonly down to pipework being undersized.

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Thanks boacelt. I had been told this by the servicing engineer, but he also explained that this is somewhat an unrealistic regulation and is rarely achieved when there is a great distance between meter and boiler - even with 28mm pipework. Only repeating what he said, but yes you are technically correct

You can expect around 2.5mbar drop from the inlet of the boiler isolation cock to the gas valve test point on ecotec models. However with cooker running your losing 6mbar. Although its unlikely to ever cause a problem, the pipework is either undersized or restricted and should have been taken care of at installation.

Strictly the gas inlet pressure should be checked with all appliances on full power according to our regulations.

However, thats not very realistic of the usual practical situation.

There is also another aspect relating to your particular boiler. The gas inlet uses a rather undersized flexible tube which loses about 2-3 mB between the boiler inlet underneath and the gas valve.

Its a bit academic if there is 18 mB at the gas valve under normal conditions.

Generally your boiler does need a 28 mm supply pipe unless its less than two metres long.

Upgrading as much of the pipe as possible will improve the situation but as the boiler will be working correctly anyway its up to you to decide if you want to bother.

Tony

Agile said:

Strictly the gas inlet pressure should be checked with all appliances on full power according to our regulations.

However, thats not very realistic of the usual practical situation.

There is also another aspect relating to your particular boiler. The gas inlet uses a rather undersized flexible tube which loses about 2-3 mB between the boiler inlet underneath and the gas valve.

Its a bit academic if there is 18 mB at the gas valve under normal conditions.

Generally your boiler does need a 28 mm supply pipe unless its less than two metres long.

Upgrading as much of the pipe as possible will improve the situation but as the boiler will be working correctly anyway its up to you to decide if you want to bother.

Tony

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Thank you Tony. Your reply was very helpful and helps me to understand much more what the regulations stipulate. It seems that I've come across two completely independent engineers that have combined together to leave me with a little dilema about what I do next with my pipework. It seems however that in the short term the problem is not unsafe, so I may choose to leave this until the summer.

It would also seem that because of the narrow flexible pipe in the boiler itself, then technically the pressure at the gas inlet is 20-21Mb, which is nudging close to the 1mb drop required by the regulations. Shame it's not possible to test directly at the inlet as the reading that I am taking could be misinterpreted if you didn't know this nugget of information.

On a semi-unrelated matter, do you know whether this issue will be picked up in a HIPS report if I were to sell the house?

mickyg said:

You can expect around 2.5mbar drop from the inlet of the boiler isolation cock to the gas valve test point on ecotec models. However with cooker running your losing 6mbar. Although its unlikely to ever cause a problem, the pipework is either undersized or restricted and should have been taken care of at installation.

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Thank you Mickyg. Very useful information, which at least I don't need to sort out very quickly. I may leave it until the summer to sort out then.

Given the point you've made about the 2.5mb drop because of the 'issue' with the ecotec models, then I'm probably getting 21.5mb at the gas inlet (with the boiler at full demand) and 18.5mb with the cooker also activated.

A.

The main issue here could be with the cooker. There should be no pressure drop at the cooker when the boiler fires. If there is the cooker may not cook properly. We had a case recently where a customer got food poisoning because her oven hadn't been getting hot enough after a new boiler was installed.

swbjackson said:

The main issue here could be with the cooker. There should be no pressure drop at the cooker when the boiler fires. If there is the cooker may not cook properly. We had a case recently where a customer got food poisoning because her oven hadn't been getting hot enough after a new boiler was installed.

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Thanks swbjackson. Fortunately the over is an electric convection oven, so it's only the hob where there is a flame. In addition to that my wife tends to burn all our food anyway!!

Thats an interesting senario described above!

However, in this case its unlikely because 16 mB at the gas valve would equate to about 18.5 mB at the connection under the boiler. Thats pretty close to the cooker's expected inlet pressure of 20-21 mB.

Of course we dont know what gas pressure would be at the cooker because thats a different pipe!

What can be done is to watch a burner flame when the boiler comes on to heat hot water. It should not change too much in size.

Tony

amardeem said:

The pressure at the meter is now 22mb (boiler on full demand) and the reading at the boiler is 18Mb - I know I've measured it myself (I know I shouldn't but it seemed the only way to satisfy myself). Although the 4mb drop from meter to boiler is a little above what an ideal installation would be, it's acceptable for the Vaillant 837 boiler, which should read between 17mb and 25mb when on full demand.

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You only 'appear' to have a 4mBar drop, in reality with your ecotec plus loosing 3 mBar betweenthe boiler gas cock and the inlet test point on the gas valve, you have the required 1 mBar drop.

What I have learned from this is that my service engineer was far too quick to assume that the pipework from meter to boiler was defective. National Grid are more than willing to come out and look at things and makes some tweeks and this costs absolutely nothing at all.

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Sounds like a lazy toad to me. Anyone servicing a gas appliance should call NG in if the WP at the meter is outside the accepted range.

Agile said:

Thats an interesting senario described above!

However, in this case its unlikely because 16 mB at the gas valve would equate to about 18.5 mB at the connection under the boiler. Thats pretty close to the cooker's expected inlet pressure of 20-21 mB.

Of course we dont know what gas pressure would be at the cooker because thats a different pipe!

What can be done is to watch a burner flame when the boiler comes on to heat hot water. It should not change too much in size.

Tony

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Hey Tony,

Thanks again for your very helpful advice. I checked the hob as you suggested and I could hardly notice the difference in the flame when turning the hot water on/off. I tried it about 10 times and in all honesty there was probably only one time out of that where I noticed any change and that was very subtle.

A.