Boiler pressure normally rises a little as heating water warms and expands, then falls as the system cools. If an Ideal boiler’s pressure climbs overnight while the heating is off and cold, keeps moving towards the high end of the gauge, or reaches the safety-valve area, that is not a normal heat-up pattern. Common fault areas include a filling connection that is not fully closed, an expansion-vessel problem or, on a combi, an internal path allowing mains water into the heating circuit.
Record cold and hot readings rather than repeatedly bleeding radiators. Do not remove the case, recharge an internal vessel or cap a discharge pipe.
What pressure should an Ideal boiler show?
Ideal Logic Combi2 user guidance says the system’s original installation pressure is normally in the 1–2 bar area and instructs users topping up that model to stop at 1–1.5 bar. Your exact model and installation may differ, so use its own user guide and the pressure originally set by the installer.
A single reading means less than a pattern. Record pressure when the system is fully cold and again after normal heating. Do not compare a hot reading with a cold target as if they are the same condition.
Is some pressure rise normal when heating runs?
Yes. Water expands as it heats, and the sealed system’s expansion vessel is designed to accommodate that change. A modest rise that reverses as the system cools can be normal.
A large swing, a climb towards 3 bar, discharge outside, or pressure that continues rising with the system cold needs investigation. The amount cannot be judged safely without the model, system size and cold starting pressure.
Why might pressure rise overnight?
If the heating has definitely been off and the system is cold, thermal expansion is less likely to explain a steady overnight increase. The key question becomes whether water is entering the sealed heating circuit from the mains or whether a previous hot pressure is taking time to settle.
Check the programmer history and whether frost protection may have fired the boiler. Ideal boilers can operate frost protection automatically in low temperatures, so “off at the thermostat” does not always mean the appliance never heated.
Check the filling-loop controls are closed
On applicable models, Ideal’s user guide shows both filling controls returned to their closed positions after topping up. If a control is left open or does not seal, higher-pressure mains water can continue entering the heating circuit.
Only check controls that are clearly identified in the exact user guide. Do not force stiff valves, loosen fittings or guess between gas and water controls. A removable filling loop should be handled only as the manufacturer describes.
What if pressure rose after topping up?
The system may simply have been overfilled, or the filling control may not have returned fully closed. Record the cold reading and compare it with the target in the model’s guide. Do not keep releasing water and refilling it in a cycle.
If the pressure rises again without another top-up, arrange diagnosis. Repeatedly correcting the gauge hides the pattern and introduces fresh water into the heating system.
Could the expansion vessel be involved?
The expansion vessel contains a compressible cushion that accepts the increase in water volume as the system heats. Ideal’s Logic service literature includes model-specific procedures for checking, recharging and replacing that vessel, and states that larger system volumes may need additional capacity.
If the vessel has lost charge, is damaged, isolated or too small for the system, pressure can rise sharply during heating and fall again when cold. Overnight cold rise alone may point elsewhere, but the whole pressure pattern must be assessed.
Can I recharge the expansion vessel myself?
No. A meaningful vessel check requires the water side to be at the correct condition and the vessel to be assessed against the manufacturer’s data. On many boilers it is inside the sealed case.
Pumping air into an accessible valve without following the correct procedure can give a misleading reading or damage the valve. Leave recharging and sizing to a competent engineer.
Could a combi plate heat exchanger cause rising pressure?
On a combi, mains domestic water and sealed heating water pass through separate channels in the plate heat exchanger. An internal failure could allow the higher-pressure mains side to feed the heating circuit, causing pressure to rise even while the heating is cold.
This is one possible professional diagnosis, not something the gauge proves. Do not isolate random valves or dismantle the heat exchanger. An engineer can test the system and distinguish it from a filling-loop or expansion problem.
What does the 3-bar area mean?
The cited Ideal Logic Code Combi ESP1 service data lists a non-adjustable safety valve set to lift at 3 bar. This protects the system from excessive pressure; it is not a normal target pressure.
If water appears from the external safety discharge pipe, do not block or cap it. Keep people away from hot discharge and arrange repair. After operating, a safety valve can sometimes continue to pass water and must be assessed.
Could the pressure gauge be wrong?
A faulty gauge or sensor can misreport pressure, but do not assume that when the reading is high. Compare an electronic display and mechanical gauge if your model has both, and tell the engineer about any disagreement.
Visible discharge, leaks or large changes should be treated as real until checked. Testing the gauge requires professional equipment and safe access.
A useful overnight observation
- When the system is fully cold, photograph the pressure and time.
- Confirm the normal programmer is not calling for heat.
- Check the identified filling controls are closed without forcing them.
- Do not top up or bleed radiators during the observation.
- Photograph the pressure again in the morning before heating starts.
- Note whether frost protection may have operated overnight.
Stop the observation if pressure enters the high zone, water discharges, a leak appears or the boiler behaves abnormally.
Safe checks a homeowner can make
- Record cold and hot readings with times.
- Check the exact Ideal model and user-guide pressure range.
- Confirm clearly identified filling controls are closed.
- Look for visible leaks without removing covers.
- Check the external discharge pipe from a safe position.
- Note recent topping-up, radiator bleeding or plumbing work.
- Record whether the rise happens only during heating or also when cold.
What not to do
- Do not keep bleeding radiators to reduce high pressure.
- Do not repeatedly top up afterwards.
- Do not remove the boiler case.
- Do not recharge or replace the internal expansion vessel.
- Do not force filling-loop valves.
- Do not cap the pressure-relief discharge.
- Do not drain hot water from the system.
Why repeatedly bleeding water is not the answer
Bleeding can lower the reading temporarily but does not stop water entering through a passing filling connection or internal fault. It can also mask the hot-to-cold pressure swing that helps diagnose an expansion problem.
Fresh top-up water introduces oxygen and minerals. The correct response is to find why the pressure rises, not to create a daily drain-and-refill routine.
What an engineer may investigate
An engineer can verify the gauge, confirm the cold fill pressure, check that the filling arrangement isolates properly, assess the expansion vessel charge and capacity, inspect the safety valve and look for an internal route between mains and heating water on a combi.
They can also check whether system volume has changed after radiators or extensions were added. The repair depends on measured evidence and the exact Ideal model.
What if pressure rises only when heating is on?
A temperature-related rise focuses attention on cold starting pressure and expansion accommodation. Record the cold value, maximum hot value and how fully it falls after cooling.
A steep rise towards the safety-valve setting is not something to manage by turning the thermostat down. Arrange a proper vessel and system assessment.
What if pressure rises when the boiler is off?
Confirm that the system truly remains cold and that frost protection has not run. A continuing cold rise makes unintended filling from the mains an important possibility, through the filling arrangement or an internal combi fault.
Do not isolate unlabelled valves to test this. Give the engineer the overnight readings and any recent top-up history.
When is high pressure urgent?
Switch the boiler off and arrange prompt help if the pressure approaches or reaches the high end of the gauge, water discharges continuously, a leak appears, the casing or pipework moves, or water is near electrical components.
If you smell gas, leave the affected area and call the National Gas Emergency Service on 0800 111 999 from a safe place. A pressure-gauge problem does not change gas-emergency advice.
What to tell the booking team
- the full Ideal model and boiler type;
- cold, hot and overnight pressure readings;
- the times each reading was taken;
- whether heating or frost protection ran;
- when the system was last topped up;
- whether filling controls are fully closed;
- any water from the external discharge pipe; and
- recent radiator, boiler or plumbing work.
Frequently asked questions
Why does my Ideal boiler pressure rise overnight?
If the system remains cold, water may be entering the heating circuit through a filling connection or, on a combi, another internal route. Frost protection and the timing of readings must also be considered.
Is pressure meant to rise when heating is on?
A modest rise is normal because water expands as it heats. A large rise towards the safety-valve area needs investigation.
Should I bleed a radiator to lower it?
Not as a repeated fix. That can hide the cause and leads to more top-up water being added later.
Can I use the boiler near 3 bar?
Three bar is the cited safety-valve setting on an applicable Ideal range, not a normal operating target. Switch off and seek advice if pressure is approaching it or discharge occurs.
Related boiler-help guides
- Boiler pressure too high
- Pressure rises when heating is on
- Boiler pressure keeps dropping
- Water from the boiler discharge pipe
Is your Ideal boiler pressure climbing overnight?
Book a fixed-price Incredaboil repair so the filling route, expansion vessel and sealed system can be checked properly.