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Published by Mo's Plumbing and Heating
How Do I Repressurise a Worcester Boiler?
Worcester Bosch is the most common boiler on Glasgow walls and it is also the one people most often cannot top up, because the filling arrangement is built into the boiler rather than hanging underneath it, and it changed across model generations. Find out which one you have and the job takes ninety seconds.
The Short Answer
Almost all Worcester Greenstar models use a filling key or a built-in filling link on the underside of the boiler rather than an external braided hose. Drop the front flap, look underneath, and you will find either a small plastic key sitting in a slot, or a keyed link with a captive handle. Turn the boiler off, engage the key, turn slowly until you hear water and the gauge reaches about 1.2 bar, then return it to the closed position. The variation between models is where the key lives, not how it works.
Start With the Model Number
Worcester has used more than one filling arrangement across the Greenstar range and its predecessors, and generic advice written for one generation is exactly why people end up convinced their boiler has no filling point. It has one. It is probably not where the article you just read said it would be.
Get the model name and serial number first, because everything else follows from it. Drop the front flap or look at the underside of the case for a printed label, and you are looking for something like Greenstar 25i, 30i, 24i Junior, 28CDi, 34CDi or Si Compact, along with a serial number. Write both down. Worcester publish model specific instructions and the manual for almost every unit they have made is available free, which is worth more than any general guide including this one.
Broadly there are three arrangements you will meet. A separate plastic filling key that slots into the underside and turns, used across much of the Greenstar range. An integrated filling link with a captive lever or handle that stays attached to the boiler, common on later models, which removes the losing-the-key problem entirely. And on some installations, particularly older or where the boiler was fitted into an awkward space, a conventional external braided loop underneath, exactly like any other make.
The Keyed Filling Link
This is the arrangement most people are asking about. Underneath the boiler there is a moulded plastic housing with a slot, and a small key, usually white or grey, that goes into it. The key is often clipped to a bracket on the underside or tucked inside the front flap when the boiler is installed, and it is frequently missing on any property that has changed hands.
- Turn the boiler off at the front control and ideally let it cool for an hour so the reading you finish on is a true cold reading.
- Locate the filling link on the underside, towards the front on most models, and note its current position. There is usually a moulded arrow or an open and closed marking.
- Insert the key fully. It should seat with a small positive click or come to a definite stop. A key that is only part engaged will turn without doing anything, which is the commonest reason people conclude the link is broken.
- Turn slowly, a quarter turn at a time. You are listening for water rather than watching the gauge at this stage, and the sound arrives before the needle moves.
- Watch the gauge to about 1.2 bar, or nearer 1.5 if your radiators are two floors above the boiler. Close as you approach it, since the reading continues to settle for a few seconds.
- Return the key to the fully closed position and remove it. Leaving a filling link part open is how a Worcester ends up at 3 bar and discharging outside, and it is not obvious by looking.
- Turn the boiler back on. If it had locked out on low pressure it will usually clear itself, and if not, hold the reset until it restarts.
If There Is No Key
Very common, and not a reason for a callout. Worcester filling keys are inexpensive and available from merchants and directly, but they are model specific, so the model number you wrote down earlier is what you order against. Buying the wrong one is the usual outcome of guessing from a photograph.
Do not improvise. A screwdriver, pliers or a key from a different appliance will turn the mechanism sometimes, and will crack the plastic housing a fair proportion of the time. That housing is part of the boiler's internal pipework rather than an accessory, so cracking it turns a two pound part into a genuine repair with the front off.
It is worth buying a spare while you are at it and taping it inside the front flap. That is where it will be looked for in five years by whoever lives there next, and it costs almost nothing to leave behind.
What the Fault Codes Are Telling You
Worcester boilers show a code on the display when they stop, and the pressure related ones are worth recognising so you can tell a pressure fault from something else before you start hunting for a key.
The main thing to understand is that a low pressure lockout code is the boiler reporting a condition rather than reporting a broken part. Restore the pressure and the code clears, often without a reset. If a code persists after the gauge is correctly back at 1.2 bar and the system has been given a moment, then the fault is not pressure and topping up further will not help.
Codes vary between models, which is the recurring theme of this whole guide, so the number on your display should be read against your own manual rather than a list someone assembled for a different unit. What is consistent is the logic: pressure codes clear when pressure is restored, and anything that does not clear is a different conversation.
Worth noting the code before you do anything. Once you have topped up and reset, the evidence is gone, and if it happens again the code you saw the first time is genuinely useful information.
How Often Should a Worcester Need This?
Once or twice a year is normal, the same as any other sealed system, and there is nothing about the brand that makes it lose pressure faster. If yours needs topping up monthly, the brand is not the reason and the cause is the same short list as for any boiler: a leak you can see, a leak you cannot, or an expansion vessel that has stopped absorbing expansion.
The one thing worth flagging on these specifically is that because the filling link is integrated and easy to leave slightly open, the overpressure version of the problem is a little more common than on boilers with a loop you physically disconnect. If a Worcester is repeatedly running high and discharging outside, check the link is fully closed before assuming the vessel has failed. It is a thirty second check that saves a visit reasonably often.
Why One Close Has Four Different Worcesters In It
The practical reason model identification matters so much here is that Glasgow's boiler stock was not installed in one wave. Flats within a single close change hands and get refurbished independently, so one stair can easily hold boilers fitted across fifteen or twenty years, several of them Worcesters from different generations with different filling arrangements.
That has a specific consequence worth knowing: asking your neighbour how they do theirs is unusually unreliable advice in this city, even though it is the most natural thing to do and even though both of you have a Worcester. The instructions that work one floor down may not apply to yours, and a confident neighbour with a different generation of the same brand has sent more than one person hunting for a key that was never fitted to their model.
The second local factor is where these things get installed. Flat conversions put the boiler where the flue could go, which frequently means a kitchen wall unit with the underside of the boiler sitting above a worktop or inside a cupboard at head height. Worcester's integrated filling links are designed to be reached from below, and reaching up into a cupboard to find a small slot by feel is a different job from crouching under a boiler in a utility room. A phone torch and a mirror, or a phone camera pointed upwards, is the trick most people arrive at eventually.
We are manufacturer certified for Worcester Bosch alongside Vaillant, Baxi, Ideal and Vokera, so these are boilers the team is on every week. That mostly matters for repairs and warranty work rather than for topping up, which is a customer job on any brand, but it does mean the model specific quirks are familiar rather than looked up on arrival.
When to Call Someone Out
Topping up is yours. Worth a call when the filling link will not turn with the correct key properly seated, when the housing is cracked or weeping, when a fault code stays on the display after the pressure is correctly restored, or when the system will not hold what you put into it. Mo and Muhammad are both Gas Safe registered and work on these regularly, and having the model name and serial number ready when you ring shortens the visit, because the right part can come on the van rather than being ordered after a look.
Boiler Repair in GlasgowCommon Questions
Usually built into the underside rather than hanging below it as a separate hose. Drop the front flap and look up at the base of the boiler for a moulded plastic housing with a slot for a key, or a link with a captive handle. Some installations do have a conventional external braided loop instead, particularly older ones or where the boiler went into an awkward space.
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Read Next
Full guide
What Should the Pressure in a Boiler Be?
On a sealed system, which is nearly every combi and most modern system boilers, aim for 1.0 to 1.5 bar when the heating has been off for a few hours and the system is cold.
How to Repressurise a Boiler
Turn the boiler off and let it cool.
Why Does My Boiler Keep Losing Pressure?
The water is leaving through a visible leak, through a leak you cannot see, or through the safety valve to the outside because the expansion vessel has failed.
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