QUESTION

My Worcester CDi boiler pressure is low. How can I fix it?


curated by 434 crowd contributors

We pulled together 9 of the most popular web sites to create this page, including www.worcester-bosch.co.uk, www.automatedhome.co.uk, in.answers.yahoo.com. We've organized their information into the most commonly discussed topics below, ranging from Overheating or pressure drop to Contact. A total of 36 crowdworkers were involved during the process, of which 13 of them gathered the information, 23 of them organized the information by different topics, and 0 of them synthesized the information into this article.


Overview

Overheating or pressure drop: Adjust the operating pressure to within a specfic range. Drain water out of the radiators. Be aware of tubes that are not completely filled.

Managing water pressure: Increase the water pressure to 2 bar. Check automatic air vent inside the boiler casing. Also check the pressure in the expansion cylinder.

Check radiaor valves: The problem on your radiators could be rot, which in turn, creates hydrogen. To find out, locate the drain valve and open it slowly. Check all joints for signs of damage and ensure there are no leaks.

Filling: Find the white arrows. Turn the key to the left. Pull the key straight down to remove. Turn the white knob to the left, filling the system.

Check pressure relief valve: How to fix low boiler pressure.

Boiler overheating: A quick summary of what to do if your Boiler is overheating. There are only a couple steps to checking it to entirety. Make sure to read all steps to ensure all problems are fixed.

Leaks: Ensure there are no leaks or overheating in any pipework or any overheating or pressure drop. If everything looks good, you might have to check if there is a leak on your central heating system.

Prv discharge: How to fix low boiler pressure.

Heat exchangers: The heat exchanger may be clogged up. Check the hot water sensor. Check the diverter valve.

Pressure release: How to fix low boiler pressure.

Bleeding the radiator: The subtopic is maintaining/outfitting boilers and how specifically to install a pressure valve in it.

Moisture in pcb: Voltage Connector Repair and Concerns

Add inhibiter: The best solution is to add an inhibiter to the system.

Contact: Contact the local accredited installer. Get the professionals to fix it. Doing it yourself risk having more problems.


Overheating or pressure drop

Overheating or pressure drop

Adjust the operating pressure to within a specfic range.

The best operationg pressure for the 28CDi is between 1 and 1.5 bar pressure. If the pressure drops below 1 bar as you have done, use the filling key to re-pressurise the boiler, but to no more than 1.5bar.
A setting of 2mb will not cause any harm when you fire the boiler up it will drop to around 1.5mb. As you have a pressurised system, the settings above must be maintained

If the pressure is above 1.5bar when the boiler is not working, you can resolve the issue by draining a small amount of water out of one of your radiators (usually the first in the circuit). The boilers pressure gauge is set to 3 bar.

The thumping sound was the sound of the boiler overheating due to lack of completely water filled tubes, so steam was formed; the pressure built up and the steam bubbles burst. If that goes on for very long, it ruins the heat exchanger and the tubes leak. Leaking tubes will cause the boiler pressure to drop. Further overheating of the tubes, now empty of water, will get hot enough to warp and sustain metalugical damage.

Managing water pressure

In order to prevent failure of heating, you can increase the water pressure up to two bar. To increase the pressure, use the key, insert, and turn, and the water pressure should increase.

First, it is worthwhile to check the pressure in the expansion cylinder, which should be about .5 bar or 7.5 p.s.i. If the bladder inside the cylinder is deflated, it cannot absorb the water expansion in the radiator system when it is hot and water is expelled from the system. When the system cools, the pressure will be low, perhaps to the extent that the low pressure switch disables the system. To check this, turn off the main supply to the boiler. Turn the red test knob a quarter turn, so as to reduce the system pressure to zero on the gauge. Check the expansion cylinder pressure on the schrader valve using a tire pressure gauge. Add pressure if necessary, using a foot pump to achieve 0.5 bar.

If your pressure vessel has failed, there is no place for expanding water to go other than out of the pressure relief valve. One temporary fix until you get a new pressure vessel is to shut off one large radiator and drain it until it is empty. If this is difficult, removing the bleed screw can help. Afterward, refit the bleed screw and turn on the valves. You now have a pressure vessel in the radiator full of compressible air. Check the automatic air vent inside the boiler casing. Loosen the cap on the top to allow the valve to work.

If you can locate the valve, there will be a knob on the top that is usually red. Turn on the filling loop to the boiler then, turn the knob which lets water out as quickly as it comes in. Do this a few times and the valve may re-seat.
If you turn a tap on and the red light with the tap symbol does not come on, then either the diagram or the microswitch are at fault. If this is the case, change the whole diverter. If the expansion vessel is dripping water, it likely needs replacing. Simply cap them off and fit a remote vessel.

Top-up the pressure in your heating system and turn it on. Keep an eye on the pressure gauge, if the needle goes straight up to three bar or over and then drops, this is the problem.

Check radiaor valves

Try to find the drain valve on your system and connect a hose, pipe, or use a bowl depending on valve positions. Open valve a little at a time, periodically checking on the gauge.

If you slowly and carefully go around ech radiator with your hands you'll find your answer.

It could be your sytem starting to rot, creating hydrogen.

Check all visable joints, including radiator valves and connections, for obvious signs of leakage. Ensure there are no leaks to any under-floor pipework.

Filling

The WB fillers are a bit special. If you do it right they will never seize, but if you do it wrong they break. Ideally you would simply have a universal filler installed; the small price difference is worth it.
It's possible to manually fill it up, but I don't really think that that is great as it doesn't solve the problem permanently.

Further over eating of the tubes, after they are empty of water, can cause them to get hot enough to warp and sustain metallurgical damage

Two considerations: first, are you sure it's a sealed system? A lot of 28cdi's were fitted as an open system. Second, the pressure on the gauge has nothing to do with the flow at the taps.

Locate the white arrows moulded into the shaft of the T-shaped filling key and the padlock symbols on the outside of the manifold.

Turn the filling key to the left so it stops and the arrow lines up with the open padlock symbol and pull the key straight down to remove.
Turn the white knob to the left, allowing the water to fill the system. Please ensure the key is fully inserted because water may drip out if it is not fully inserted.

Check pressure relief valve

Check the automatic air vent in side the boiler casing; it has a little cap on the top and should be loose to allow the valve to work.

Check that there is no water being discharged from the pressure relief valve (sometimes referred to as an overflow). This pipe usually goes from the boiler through to an outside wall and terminates outside.
Check this for signs of dripping. If it is wet, this may mean that the pressure relief valve is faulty.

Your pressure vessel has failed and now there is no place for expanding water to go other than out the pressure relief valve

Boiler overheating

Boiler overheating

A quick summary of what to do if your Boiler is overheating.

First, ensure the boiler is turned off and the heating system has cooled down.

Your boiler may have a metal, slatted cover panel on the underside--this will need to be removed by pulling down the front edge and sliding it towards you.

The internal filling link assembly, if fitted, is a black plastic moulding on the left hand side, on the bottom of the boiler.
It is connected to the DHW (domestic hot water) inlet connection and the CH (central heating) return connection.

If there are damaged air pressure tubes (i.e., sticking or slow fan) or if there is sticking air pressure, check if the restrictor has been removed

Leaks

Ensure that there are no leaks to any under-floor pipework and check there is no overheating or pressure drop.

It also could be a leak on your central heating system so make sure to check that as well.

Prv discharge

PRV discharge

How to fix low boiler pressure..

Earlier plate heat exchangers can pinhole internally, causing most of the pressure to go into central heating. This would result in 3-bar pressure on gauge and discharge from the PRV. Also, check that the expansion vessel diaphragm has not perished.

There should be a small (15mm) copper pipe running through the wall near your boiler to the outside. If this pipe is dripping, your PRV will need to be replaced.

Heat exchangers

Heat exchangers

The heat exchanger may be clogged up.

Plate heat exchangers can block with magnatite. One thing you should check is the hot water sensor for correct resistance.
. The diverter valve can pass down the heating pipe when in hot water, in turn giving poor hot water. This requires a new valve or service kit inside valve.
.
By the sound of things, if your hot water takes that long to heat up and the boiler is making noises when you run the hot water, I would say your heat exchanger is getting clogged up.

Pressure release

There are several possible causes.
1) Your expansion vessel could have lost pressure.
2) The valve is faulty.
If 1 and 2 do not apply; check the pressure release valve where it terminates outside for signs of water drops.

Bleeding the radiator

2 bar is ok though it may move up a little when heating is on. If you really want to decrease pressure, you have to let some water or possibly air out.
First, try to bleed your radiators; stop bleeding when water comes out.

Try to bleed the radiator so the bar drops down to somewhere in between 1.5 & 2. Also make a note of Worcester's number, just in case.

Shut off one large radiator and drain it until empty; removing the bleed screw helps, then re-fit the bleed screw and turn on the valves. You now have a pressure vessel in the radiator

Moisture in pcb

moisture in PCB

Voltage Connector Repair and Concerns.

If there is excess mousture, the problem may be that the low voltage connector on the PCB has a faulty sensing electrode/lead. Another problem may be a sticking gas valve, or that the gas is incorrectly set low.
Finally, the central heating knob Spindle can snap on the PCB.

Add inhibiter

Add inhibiter

The best solution is to add an inhibiter to the system.

The best solution is to add an inhibiter to the system.

Contact

Contact

Contact the local accredited installer.