Mitsubishi Ecodan System Pressure Changes - An Issue or Expected ?
Hi all
I've noticed that my 8.5kw Mitsubishi Ecodan PUHZ-W85VA2 heat pump w pre-plumbed 250L DHW cylinder EHPT25X-UKHCW system pressure changes depending on the mode of operation.
- Heating on AutoAdaptation flow temp circa 40C = system pressure 1.5bar
- Antifreeze mode flow temp circa 20C = system pressure 0.5bar
- System off = system pressure 0bar
Is this normal/expected ?
If not, what could be the cause and how would you go about fixing it ?
I've had this system 7 years and first noticed this about a month ago.
Photo/screenshots from MelCloud attached.
No obvious performance issue noted.
THANKS !
Hello, this sound like expansion and low on water pressure, assuming you have a 2 story house you should have a static pressure of around 1 bar, running pressure of around 1.2 bar and antifreeze mode of between 1 bar and 1.2 bar, the vessel should balance and absorb expansion.
To check this you will need to switch of the system and safely electrically isolate, isolate the expansion vessel and drain it, then using a pump with a gauge pump this vessel through the valve usually at the top to 1.5 bar, place this back into position and refill the system to 1 bar. then fire the unit back up.
If the vessel will not hold its pressure its likely that the bladder is broken and this will need replacing. there are some rules in the UK:
2. Servicing Requirements for Expansion Vessels
A. Regular Maintenance Checks
-
Annual servicing is recommended, often carried out alongside a boiler service.
-
A service should include:
-
Checking pre-charge pressure of the expansion vessel (usually between 0.75 - 1.5 bar).
-
Re-pressurizing if necessary using a foot pump or nitrogen (as per manufacturer’s instructions).
-
Inspecting for leaks, corrosion, or diaphragm failure.
-
B. Signs of a Failing Expansion Vessel
-
Frequent pressure drops in the heating system.
-
Water leaking from the pressure relief valve (PRV).
-
Boiler pressure gauge rising too high when heating is on.
C. Replacement and Repair
-
If an expansion vessel fails (e.g., diaphragm rupture), it must be replaced.
-
Some vessels have external Schrader valves for easy re-pressurization, while others may need complete replacement.
3. Who Can Service an Expansion Vessel?
-
For sealed heating systems, a qualified heating engineer or plumber can service the vessel.
-
For unvented hot water cylinders, only a G3-qualified engineer can work on the expansion vessel.
4. Compliance & Best Practices
-
Always follow the manufacturer's servicing guidelines.
-
Ensure servicing records are kept, especially for landlords (required under the Landlord and Tenant Act 1985).
-
Commercial systems may have additional requirements under The Pressure Systems Safety Regulations (PSSR) 2000.
Expansion is important for the system to run correctly so it may be worth getting a qualified engineer if you are not sure.
Professional installer. Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.
@ashp-bobba thanks ! Ok so it's likely the expansion vessel. It's been replaced twice already. Last time about 2yrs ago. Will get in touch with a local heating engineer (again).
@alsocold123456 I would have thought it would last a bit longer than that. Its worth checking out, it may have just lost some air pressure, this is something your service engineer would have checked on the last service.
Professional installer. Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.
-
Ecodan consuming 100kwh per day in new build!!!
4 weeks ago
-
Efficiency Concerns on newly installed Mitsubishi Ecodan 8.5kW
4 months ago
-
Ecodan 11.2kw Wireless thermostat drop outs
4 months ago
-
Transforming a Derbyshire Property into an Energy-Efficient Haven
5 months ago
-
Ecodan ASHP - How to optimise my set up?
5 months ago
Currently viewing this topic 1 guest.
- 26 Forums
- 2,123 Topics
- 46.7 K Posts
- 32 Online
- 4,531 Members
Podcast Picks
Latest Posts
-
RE: Octopus Cosy & Octopus EV + bidirectional smart tariff, together. What, eh?
I've certainly seen that on their Ts & Cs page but ...
By Majordennisbloodnok , 4 hours ago
-
RE: Planning Permission May 2025
Where does it state this please? Im genuinely interest...
By JamesPa , 7 hours ago
-
RE: ASHP heat output monitoring
@carlo - not much better, is it. It looks more like a u...
By cathodeRay , 9 hours ago
-
RE: Renewables & Heat Pumps in the News
this document extensively describes (in a non-blame, ne...
By Judith , 12 hours ago
-
RE: Ecodan - Legionella Operation Time and Target Temperature
Once the white plastic cap is removed, my immersion loo...
By Old_Scientist , 1 day ago
-
RE: Replacing Refrigerant on Mitsubishi Heat Pump
@dgclimatecontrol I don't know, but they were not happy...
By DavidAlgarve , 1 day ago
-
RE: Why do we need pressurised systems?
A good question @toodles. My old open thermal store and...
By AllyFish , 2 days ago
-
RE: 300 Liter Tank - Do I have to heat it all?
Cross references for @martingale Background discussi...
By Transparent , 2 days ago
-
@ecobaker May I ask a question of you please. I too hav...
By Papahuhu , 2 days ago
-
RE: Share Your Experiences with Heat Pump Manufacturer Support
@terry1812 Oh Good! Pleased to help if I can! Regards, ...
By Toodles , 3 days ago
-
It's unclear to me how the Smart Control project work b...
By Transparent , 3 days ago
-
RE: Have Consumers Been Lied to About the Efficiency of Heat Pumps Made in China?
@pavel, this isn't about discrediting Chinese products....
By Mars , 3 days ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
We had an excellent four months (11/3 to 15/7) generati...
By JulianC , 5 days ago
-
RE: Is this just haze or something more?
I think the present somewhat cooler hazy days show the ...
By Judith , 5 days ago
-
RE: My misgivings about installing ASHP and solar panels via the ECO4 scheme...
All noted and accepted and as I say I am sorry that you...
By JamesPa , 5 days ago
-
I think it is very much me that is sitting outside the ...
By Grantmethestrength , 5 days ago
-
RE: Who's your electricity provider and what's your tariff?
Aggregators have been recognised for many years, and it...
By Transparent , 6 days ago
-
RE: Help me keep the faith with my air source heat pump installation
Great news I edited my previous post (probably af...
By JamesPa , 6 days ago