INTERMITTENT WATER PRESSURE LOSS

[John Taylor]

Re: Domestic c/h with Vaillant ecoTEC plus 837 boiler.

For the past 12 months or so, boiler water pressure has intermittently dropped from the normal operating pressure of 1.8bar to 0.3bar overnight, indicated by fault code F75.

I would re-pressurise the system and monitor pressure for a couple of weeks noting stable pressure then forget about it. A couple of months later, I would wake up to no-heat and/ or no-DHW and re-pressurise again. About the 3rd occassion I called out my local installer/service engineer and advised him that there had not been any slow reduction in water pressure. He did a visual search but could not find water leak.

The Vaillant service engineer was then called out and replaced faulty water pressure sensor which was 'gunged up'.

2 weeks later, same problem, woke up to no heat, water pressure at 0.3bar, code F22 this time. My local installer called out, visual search for water leak, none found. I then agreed to him adding C-Tec Miracle Seal to the system. The product information states that it is "100% guaranteed not to clog the system in accordance with application instructions."

However I have a radiator with TRV set for frost protection, which, by coincidence, won't now heat up when TVR operated to call for heat. I have checked for air-lock and bled the rad, no air or aerated water released, just lots of clear water........no sign of the coloured sealant nor sealing of the 'leaking' bleed valve!.

Before calling out my service engineer again, I am hoping this forum's experts could help with my queries viz:-

Q1 - Does anyone know of a case where adding the leak sealant can cause problems?.

Q2 - Why hasn't the sealant 'sealed' the bleed valve?.

Q3 - What is the likely reason for the rad not heating up ?.

Q4 - What other causes of loss of water pressure in Vaillant boilers are regularly recorded?.

Looking forward to your responses....many thanks.

 

[John Taylor]

Hi John,
So your highest radiator / part of heating system is over 10 Metre's above your boiler then ? Your service engineer will need to drain the boiler to check & adjust the vessel charge next service.
(Beat me to it Craig.)
Just to correct you F75 is not loss of system pressure that is the F22 you had the second time.

Thanks very much for your advice Craig and Chris. The highest rad is 1.5 metre above the boiler so I will drop the water pressure to 1.1bar as recommended by you and confirmed by my referral to the Vaillant Installation booklet. I am surprised that neither the Vailliant or my service engineer set the water pressure at about 1.1bar nor stressed that I must do the same when I needed to re-pressurise the system.

I was therefore responsible for filling the system until I saw the LED reading reach 1.8bar, well below the max of 3bar...amateur DIY experts, what should you do with them?

Re: your reference to my first registered fault code of F75 and water pressure reading [LPW] of 0.3bar, I had checked the manual's troubleshooting table for F75 which stated the following:
"Fault, no pressure change detection when starting pump - Cause: Water pressure sensor and/or pump defective, air in installation, too low water pressure in boiler; check adjustable by-pass, connect external expansion vessel to return." so I assumed LWP was the cause. As previously posted, a Vaillant service engineer visited and changed a gunged-up water pressure sensor but as you can see, since then, the problem persists.

By reducing the water pressure to 1.1bar, is it likely that the intermittent low pressure shutdowns will stop? and/or what are the other possible causes?.

 

[chris watkins]

No, there are other underlining issue that a proper boiler engineer needs to correct / investigate when on site. Unfortunately not all the problems can be fixed by reading the Manufactures Instructions albeit that if some plumbers did at least have a thumb through they might have a better understanding of the issues.
F75 is the boiler looking for a change in the standing pressure when it starts up.