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Published by Mo's Plumbing and Heating
How Long Does It Take to Fit a New Boiler?
One day for a straight swap, two or three for anything that moves the boiler or changes the system type. The more useful question, and the one people actually mean, is how long you will be without heating and hot water, and that is a shorter answer than the job length suggests.
The Short Answer
A like-for-like combi swap in an accessible position is a single day, with heating and hot water back on the same evening. Converting from a tank system to a combi is usually two days and occasionally three. Moving the boiler to a different wall adds a day on top of whatever else is happening. On any multi-day job the water supply is normally restored each evening even where the heating is not, and that is worth confirming before the first day rather than assuming.
The Realistic Timings
Four common jobs, with the caveat that any of them can run longer for the reasons in the next section.
- Like-for-like swap, same position, same type: one day. Old unit out, new one hung on the same brackets or close to them, existing connections adapted, flue replaced through the existing hole, system flushed, filled and commissioned.
- Combi to combi with a change of make or size: still usually one day, occasionally spilling into a second morning where the pipe centres differ enough to need reworking.
- System or regular boiler converted to a combi: two days typically, three where there is a lot of redundant pipework. The cylinder comes out, the loft tank comes out, redundant runs are stripped and capped rather than left in walls, the hot supply is rerouted and the cupboard is made good.
- Boiler relocated to a different wall or room: add a day. Every service has to follow it, gas, water, condensate and flue, and the old position needs making good afterwards.
What Turns One Day Into Three
The appliance is the predictable part. Everything around it is what moves the timing, and these are the things worth flagging when you book rather than discovering on the day.
The flue route. Where the existing hole can be reused the flue is quick. Where it cannot, because the new appliance needs a different position or the old termination is no longer compliant, you are into a new core drill, a longer horizontal run, or a vertical flue through the roof. That last one can add most of a day on its own.
The gas supply, if it needs upgrading. Whether it does is a survey question and 589 covers what that does to the price. What it does to the DAY is add most of one, because the new run has to be installed, tested and the appliance recommissioned on it, and in a flat that means working between the boiler and a meter that may be two floors away in a close cupboard.
System condition. A system full of sludge needs a proper flush before a new boiler goes on it, and a power flush is a half-day job in itself. Skipping it is how a new appliance gets a blocked heat exchanger in year two, and most manufacturer warranties expect it done.
Asbestos, in properties of a certain age, particularly around an old back boiler or in flue components. If it is found, work stops until it is dealt with properly, and that is not a delay anyone can shortcut.
And access. A fourth-floor flat with no lift, a boiler in a boxed-in cupboard, or a loft position all add time before anything technical starts.
How Long You Are Actually Without Heating
This is usually the real question and it has a better answer than the job length implies.
On a one-day swap you lose heating and hot water from the morning until commissioning finishes, so one evening at most, and often it is back on by late afternoon.
On a two or three day conversion, the pattern is normally that the cold water supply is restored each night, and hot water may or may not be depending on where the work has got to. The heating usually comes back at the end rather than in stages, because the system is drained for the duration.
None of that is a rule, and it varies with the job, which is exactly why it is worth asking rather than assuming. If anyone in the house needs heat reliably, say so when the date is being set rather than on the morning. It changes how the work is sequenced and occasionally which week it is done in.
Worth planning for the cold either way. A conversion in January with the system drained for two days is a different experience from the same job in June, and the freedom to choose the month is one of the genuine advantages of planned work over a breakdown.
What Happens on the Day
Roughly the sequence, so the timings above make sense rather than being numbers to trust.
Isolation and draining first, which takes longer on a system with no drain-off at a sensible point. Then the old appliance and flue come out. On a back boiler removal this is the bulk of the job rather than the start of it.
The new position is prepared, brackets set, and the flue fitted and sealed. Then the appliance is hung and the gas, water and condensate connected, with the condensate route being the one that most often needs thought in an older property.
The system is filled, flushed and dosed with inhibitor, and a filter fitted on the return. Then commissioning: gas rate checked at the meter, burner pressure set, combustion readings taken and recorded, controls set up and demonstrated.
Commissioning is not paperwork for its own sake and it is not the part to rush. It registers the installation, validates the manufacturer warranty and produces the record you will need for a warranty claim years later.
You should finish with the manufacturer's paperwork, the warranty registered, the Building Regulations notification handled and the controls explained. Ask to be shown the commissioning readings rather than just handed the folder, because that is the one part of the handover that tells you the appliance was set up rather than simply connected.
Why an Estimate Can Move
Occasionally a one-day job becomes a two-day job and it is worth understanding when that is legitimate and when it is not.
Legitimate: something hidden turns up. A gas run that measures inadequate once tested, corroded pipework that cannot be reconnected safely, asbestos, or a flue route that fails once the wall is opened and the actual construction is visible.
Not legitimate: things that a survey should have found. Where the boiler is going, what the flue will do, the state of the system, the size of the gas run. Those are survey questions, and a survey exists precisely so that the timing and the price are known before anyone starts.
The honest position is that surprises should be rare and should be explained when they happen, with a conversation before extra work rather than a longer invoice afterwards. That is also why the free survey on installation work is worth having rather than accepting a figure over the phone.
What Adds a Day in a Tenement
Three things push installation timings out in this city more than anything about the appliance, and all three are worth raising when booking so the slot is the right length.
The flue, first and by a distance. A traditional tenement gives a rear elevation crowded with windows, a light well and neighbours' openings, all of which impose minimum distances a flue terminal has to respect. Where the straightforward route is not compliant the answer is a longer run, a different boiler position, or a vertical flue, and any of those turns a comfortable day into a long one. On a listed building or in a conservation area, which covers large parts of the West End and pockets of the Southside, what may be fitted to a visible elevation is constrained further and needs establishing before the boiler is ordered rather than after.
Second, permission. In a flatted building the external walls and the roof are usually common property, so a new flue penetration is not solely your decision. Where the building is factored, that consent goes through the factor, and it takes as long as it takes. It holds up a job that is otherwise ready, which is why it wants starting early rather than the week before.
Third, the meter and the stairs. Commissioning includes a gas rate measured at the meter, and in a tenement the meter is frequently in a communal cupboard on another landing, sometimes locked with the key held by the factor or a neighbour. Add a fourth-floor walk-up with no lift and every trip to the van is a ten minute round trip. Neither changes the work and both change the day.
The practical upshot is that a Glasgow flat installation is more variable than the same appliance in a modern house, which is an argument for a survey rather than an estimate, and for booking outside the winter peak where the choice exists.
When to Call Someone Out
Worth booking a survey rather than asking for a timing over the phone, because on this job the flue route and the state of the existing system decide the answer and neither can be established remotely. The survey is free on installations and replacements, and it is where the day count and the fixed price both come from. New boilers are supplied and fitted from £699 including VAT with the final price confirmed on the call or the visit. Mo and Muhammad are Gas Safe registered for domestic work. If anyone in the household needs heating reliably, say so when the date is set rather than on the morning, because it changes how the job is sequenced.
Boiler Installation in GlasgowCommon Questions
A day, where the new appliance goes in the same position and the existing flue hole can be reused. Heating and hot water are normally back on the same evening and often by late afternoon. A change of make or size can spill into a second morning if the pipe centres differ enough to need reworking.
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