Big pressure swing - 1 to 3.4 bar on Vaillant Boiler

[adrian_ros]

Hello.

The pressure measured on our Vaillant ecoTEC plus 630 reaches 3.4 bar. The target flow temperature is set at 61 degrees.

The pressure with the system not working (boiler and pump off) is 1.2 bar. After 30 mins pressure goes to 3.0 bar, after 60 mins to 3.4 bar.

This swing from 1.2 bar to 3.4 bar is not normal, right? What's the typical min-max pressure range for such boilers?

Ok, now a few questions please. Could there be an issue with the expansion vessel? I read that there a TRV valve is supposed to open at 3 bar. That does not happen, looks like.

The boiler has been serviced by PlusHeat about 2 months ago, but the contractor didn't stay long enough (1 hour) to check the pressure. I don't think he checked the expansion vessel. Is that something that shouls have been checked?

How serious is the situation? Should I call PlusHeat as a matter of urgency? Any advice?

To note, the boiler has episodes when it stops working because the pressure is too low. That's why I cannot bleed the system - it will go on the other extreme, where the boiler won't start (F.22 low pressure).

Many thanks!

PS Setup is with this Vaillant boiler and a big MegaFlo water cylinder.

 

[CountryFan]

No it’s not normal and you do indeed have an expansion issue. It’ll operate a PRV (pressure relief valve) not a TRV (thermostatic radiator valve). As to whether it should have been checked depends on what’s included in their service - seems like it perhaps should have been: https://www.plusheat.co.uk/boiler-service/

 

[Jurassicspark]

Either expansion vessel flat (requires a recharge), or it had seen better days and been punctured. If it's the latter then it will need replacing.

When you mention TRV, I suspect you're talking about the PRV (pressure relief valve), and by the looks of it that's doing its job and letting water exit the system, reducing the pressure, which is why you're eventually see f22 on the boiler.

Repeatedly causing the PRV to lift can result it being stuck open, so it's better if you get it inspected, though that should have been carried out during the "service".

 

[Agile]

I would expect any competent service engineer to ask questions about the pressure to see if it needs further investigation.

 

[adrian_ros]

Thank you all for the replies. Indeed, should have been PRV.

The plan is to call PlusHeat to check the expansion vessel and PRV. And whatever else they can think of.

In the meantime I have set the temperature to only 49 degrees (from original 61 degrees). With that the pressure goes up to "only" 2.5 bar.
I cannot think right now of anything else I could do until the gas engineer pays us a visit.

 

[adrian_ros]

Update: Called PlusHeat (with whom we have Master Plan: Maintenance + Emergency Plans-Annual Premium Emergency Plan (£99 Call Out)).

Have encountered resistance, the person at the other end said high pressure was not an emergency!

I persisted and someone will come today/tomorrow to diagnose first. Could be 1) expansion vessel failure and 2) PRV failure, what else could it be? I asked if possible to bring the parts in the van but they said no, first diagnose...

Question: Is +3.5 bar a serious situation or not?

An analogy: someone having high blood pressure, but the doctors saying this is not an emergency, nothing to do unless there is a stroke or heart attack .

 

[Johntheo5]

Its serious from a safety point of view if the PRV is not lifting at 3.5bar, is it??. If it is, then each time the boiler/system is cold the pressure should be a little less.

 

[Agile]

It is serious from the boiler's point of view.

If the PRV was operating then the system pressure would probably fall below the minimum needed on start and stop the boiler from starting up.

In reality the EXV { expansion vessel } probably only needs a few strokes of a foot pump to add a little air.

In many boilers the EXV is mounted behind the boiler with the air valve accessible by the user with care. However in your case I think that your model has it fitted inside where it is not accessible without opening the sealed boiler case.

But you seem to have a comprehensible boiler cover even if they are not as helpful or careful as they should be.

 

[adrian_ros]

Hi all.

To have closure on this topic - someone came and pumped the expansion vessel. There was minor drama later on as a valve wasn't closed properly and a second visit was needed two days later. Now all good.

I am keeping an eye on the pressure, see attached picture. Using an ESP32-CAM to get photos of the pressure gauge every hour, getting a snap every hour via Telegram.

Now the problem morphed into play... how to automate pressure monitoring.

Many thanks again.

 

[dilalio]

For future reference, you can sometimes drain a radiator to half way (one with manual valves like a towel rail is best) and temporarily use that as an EV... Usual caveats apply.

 

[Agile]

I do not recommend that as it can get forgotten and complicate anyone coming to deal with it correctly. But it does work for anyone without a compressor.

But then I always carry a compressor with me.

In practice boiler PRVs rarely get checked. But they are pretty reliable and usually do open around the set pressure which is usually 3.5 bar. Depending on how clean the water is their problem is that they often leak at a pressure below the set value. But pressurising to over 3.5 bar to check them can risk damaging some older rads. I have heard stories of some ballooning out. But thats when they don't just burst!

But as in a properly configured system the pressure increase from cold to hot is usually no more than about 0.5 bar and so the maximum pressure rarely exceeds 2.0 bar which is well below the PRV setting of 3.5 bar.

 

[dilalio]

I do not recommend that as it can get forgotten and complicate anyone coming to deal with it correctly. But it does work for anyone without a compressor.

But then I always carry a compressor with me.

In practice boiler PRVs rarely get checked. But they are pretty reliable and usually do open around the set pressure which is usually 3.5 bar. Depending on how clean the water is their problem is that they often leak at a pressure below the set value. But pressurising to over 3.5 bar to check them can risk damaging some older rads. I have heard stories of some ballooning out. But thats when they don't just burst!

But as in a properly configured system the pressure increase from cold to hot is usually no more than about 0.5 bar and so the maximum pressure rarely exceeds 2.0 bar which is well below the PRV setting of 3.5 bar.

@Agile the above advice was for non-plumbers who won't have or know how to use a compressor on an EV.