Why is my boiler loosing pressure weekly?

Comments (26)

Maybe the Pressure Relief Valve (PRV) is slowly letting water pass. Is there a pipe going out the wall below boiler? Check outside if this pipe has dripping water - if yes then change the PRV valve.

Your expansion vessel will of probably lost its charge of air and in turn is now blowing off through the PRv valve

If yes get a Gas safe engineer to replace

The expansion vessel needs re-pressing

Lots of causes but a few to check is PRV as mentioned. Perforated plate heat exchanger if its a combi. Expansion vessel, radiator valves. It does take much water loss to drop pressure. Also worth checking for a hole in the primary heat exchanger by turning the boiler off for a few hours and checking nothing comes out of the condense pipe. Also try isolating the boiler heating pipes for a while to see if the loss is within the boiler or elsewhere.

Lots of causes but a few to check is PRV as mentioned. Perforated plate heat exchanger if its a combi. Expansion vessel, radiator valves. It does take much water loss to drop pressure. Also worth checking for a hole in the primary heat exchanger by turning the boiler off for a few hours and checking nothing comes out of the condense pipe. Also try isolating the boiler heating pipes for a while to see if the loss is within the boiler or elsewhere.

Has the heat exchanger been checked inside. The condensate pipe will run with the boiler off?

Expansion vessel needs charging normally about 1.5bar

It is the Expansion vessel +PRV, or your main heat exchanger is leaking or tiny leak from the pipe work +TRV’s There must be some investigation done to get the right one.

Most likely its expansion vessel and prv

Expansion Vessel or Pressure Relief valve or even a leak in the heating system without looking at it’s just guesswork

It doesn't take much of a leak to loose pressure in the boiler.check radiators for any sign of a leak or drips

There is only a few reasons why this can happen 1. Leaking pipework including valves and radiators. This would show itself in the flat beneath. It would be worthwhile having a conversation with your neighbours 2. Leaking Pressure relief valve (PRV) due to the expansion vessel losing its charge. The PRV normally discharged outside and would normally be situated approximately a metre below the flue outlet 3. You have a crack or pinhole in the main heat exchanger. This would result in water dripping out the condensate pipe when the boiler is switched off. 4. A leak inside the boiler casing. This would show a leak inside the property around the boiler. I would suspect either 2 or 3 would be the most common. I hope this helps. Regards Bob

If the system is continually losing pressure, and you keep adding water to the system it is going somewhere. If you have access to the pressure relief pipe from the boiler ( 15 mm pipe going through wall to outside) tie a plastic bag over it to check for gradual leak. Best way to check for a leak on the internal pipework is to isolate radiator circuit at boiler and pressure test the radiator circuit. I suspect a leak in the pipework, possibly in the screed floor. Personally I use a thermal imaging camera with the heating turned up to max.

You have a leak try isolating boiler and without heating for a few days, try and determine whether it is boiler or system

Of its taking that long to go down its possibly a packing gland on a radiator the problem is it will have dried up before you ever find it

As you have explained you have had the boiler checked and the PVR and the pressure vessel, this will conclude that there is a small leak some where on the system, possible on an unseen piece of pipe work like under the floor on the ground floor. This has been the case a few times. I have found them in the concrete in the ground floor as well as no conduit tube has been used and the copper pipe gets pin holes and the water slowly seeps out.

If there is no sign of water leakage then it's most like to be the expansion vessel. I usually find repressurising them does the trick, however it may need replacing. Also worth checking pressure relief valve.

If there is no sign of water leakage then it's most like to be the expansion vessel. I usually find repressurising them does the trick, however it may need replacing. Also worth checking pressure relief valve.

when heating is on for around 30 mins, check the pressure gauge, if it's at 3 bar, expansion vessel requires re pressurising or re newing, domestic heat exchanger problems.

As stated, put a bag or bottle over PRV vent pipe and see if anything comes out after repressurising. You have not mentioned what boiler make. I find that it is very common for new Worcester boilers to often lose air from the expansion vessel. When the heating has been off for a couple of hours, and ideally in the morning, before turning on the heating go round and feel all over each rad valve and then look at your hand for any sign of water! Tony

PRV valve? and possibly leak pipe in the screed floor? either somewhere in the ground, concrete?

Let’s stop guessing and get someone to look at it quotes should be free where are you based

Pressure relief valve may be passing, to check this there will be a pipe outside near the boiler area that will be dripping water intermittently.. if not it's a leak under the ground floor or maybe a boiler issue.. more likely the earlier two tho..

Expansion vessel or leaking heat exchanger. Could possibly be a leak on system somewhere like a radiator valve but only leaking while up to temperature and evaporating while hot, so not showing.

Could be expension vessel, pressure relief valve, or secondary heat exchanger letting by