Would a boiler with low pressure increase energy usage
Hi,
I live in a rented apartment that uses a heat pump system for both heating and hot water. I've observed that the system's pressure is frequently low. Usually the highest it goes is 1.2 bar—I have seen it as low as 0.5 bar on several occasions. Although the landlord has had technicians top up the pressure multiple times over the past 5 months, the pressure consistently falls back down.
I have the thermostat permanently set to 20c/21c, and I'm concerned that the low pressure might be causing the heat pump to work less efficiently, potentially increasing energy consumption and, consequently, my energy bills.
Could you please advise:
Energy Consumption: Does operating a heat pump at a lower-than-recommended pressure lead to higher energy usage for heating the property and the hot water tank?
Diagnostics/Resolution: What could be causing the pressure to drop repeatedly, and what steps might be taken to diagnose or fix this issue?
Advice from 1 local tradesperson
? Quick Summary of Your Concerns
1. ???? Energy Consumption
Yes — low system pressure can reduce the efficiency of your heat pump, for these reasons:
• Poor heat transfer: Low pressure = less water in the system, which reduces the amount of heat the pump can transfer into your home.
• Increased run time: The system may need to run longer to reach the set temperature, using more electricity.
• Hot water tank recovery time may increase, requiring more frequent cycling.
• Air pockets from low pressure or tiny leaks can trap heat in the system, leading to pump strain or short-cycling.
So, yes — running with low pressure over time can increase your energy bills, reduce comfort, and put extra wear on the system.
2. ???? Why Does the Pressure Keep Dropping?
Repeated pressure drops usually point to one (or more) of these issues:
???? Common Causes:
1. Micro-leak in the system
• Small, often hidden leaks in pipework, radiator valves, or joints (especially under floorboards or behind units).
2. Leaking pressure relief valve (PRV)
• If the system was overfilled at any point, the PRV may be weeping small amounts of water as a result.
3. Expansion vessel failure or loss of charge
• The expansion vessel is crucial for regulating pressure as water heats and expands. If it fails or loses air charge, pressure will drop.
4. Air removal over time
• If air is slowly bleeding out of auto air vents, pressure can drop gradually without any visible water loss.
???? Diagnostics & Fix Suggestions
???? Diagnostic Steps:
• Check for visible leaks around radiators, pipes, and under hot water cylinders.
• Ask the landlord’s engineer to test or recharge the expansion vessel.
• Inspect the PRV pipe (usually outside) — if water is dripping out periodically, the valve may be letting pressure out.
• Confirm whether auto air vents or towel radiators are constantly bleeding air.
????? Suggested Fixes:
• If no obvious leak: request a pressure drop test with leak detection fluid or thermal imaging.
• Have a qualified tech check the expansion vessel — it might need recharging with air or replacing.
• Fit a leak detection fluid or inhibitor with dye into the system if the leak is very small/hard to trace.
• In extreme cases, consider installing a sealed system alarm to notify when pressure drops — especially in rented or vacant properties.
????????? What to Tell the Landlord:
Politely inform them that:
“The system pressure drops frequently, which could be reducing the efficiency of the heat pump and increasing electricity use. It’s also a sign that something is wrong — possibly a failing expansion vessel or a small leak. I’d appreciate a more in-depth inspection to avoid long-term cost or damage to the system.”
?
If you can give me the heat pump brand/model, I can give you exact pressure ranges and specs for your system. Let me know — happy to assist further!
