Pressurisation units maintain the correct pressure within a sealed LTHW heating circuit, topping up automatically as needed. ComGas installs, replaces and services commercial pressurisation units for offices, schools and commercial buildings across Surrey and surrounding counties.
A sealed LTHW heating circuit needs to be kept at the correct pressure to work properly — too low, and pumps can struggle to circulate water and air can be drawn into the system; too high, and safety valves can lift unnecessarily. A pressurisation unit automatically tops up the circuit to maintain the pressure within a set range. This is a distinct piece of equipment from a circulation pump, even though the two are often installed in the same plant room and can be confused with one another.
ComGas installs, replaces and services commercial pressurisation units within sealed LTHW circuits for offices, schools, care and residential settings and other commercial buildings across Surrey and surrounding counties. We assess an existing unit's performance and the wider circuit it serves before specifying a replacement, and coordinate this work with pumps, controls and any wider heating or plant room project.
This page covers the pressurisation unit itself, within the heating circuit. General circulation, booster and drainage pump installation is a separate service — see our Pump Installations page — and the wider LTHW circuit this unit protects sits within our broader commercial heating scope.
ComGas Services UK Ltd
Commercial pressurisation units from Farnham, Surrey.
We assess the existing unit and circuit before specifying a replacement or new installation.
Installing a pressurisation unit on a new or previously open-vented heating circuit being converted to a sealed system.
Replacing a pressurisation unit that has failed, is topping up excessively, or is no longer suited to the circuit it serves.
Servicing pressurisation units as a standalone visit or as part of a wider heating maintenance programme.
Planned. Professional. Practical.
A pressurisation unit that is frequently topping up, cycling excessively, or has failed is often a symptom of a wider circuit issue — a slow leak, an undersized expansion vessel, or a unit that was never correctly matched to the system's volume in the first place. We assess the unit and the circuit together before recommending a straightforward replacement, so we are not simply repeating a specification that was never right.
Installation or replacement is sequenced to minimise disruption to heating and hot water, and coordinated with any pump or controls work happening on the same circuit. Once complete, the unit is commissioned and its performance checked before handover, and we explain what to look out for if it needs attention in future.
Before replacing a pressurisation unit, we consider whether the wider circuit is contributing to the problem — an undersized or failed expansion vessel, a suspected leak, or pumps that are placing unusual demand on the system. We also consider access for future maintenance and how replacement can be sequenced to minimise disruption to heating and hot water in an occupied building.
Every pressurisation unit project is scoped to the specific circuit and building. We assess the wider system rather than treating the unit as an isolated component.
Education
Twin digital pressurisation units with an expansion vessel were installed with the school’s new boiler plant.
View project
Education
Wall-mounted Mikrofill pressurisation units and an expansion vessel serve the school’s new sealed heating system.
View project
Education
A pressurisation unit and expansion vessel were installed beside the school’s corridor distribution pipework.
View projectGenuine reviews from ComGas customers, submitted through Google.
Rated 5.0 out of 5 from 75 Google reviews.
"Really happy with the service! Matt came out to carry out our boiler service and was friendly, professional and did a great job."
Kerryann, Google review, September 2026
"First time we've used this company and it won't be the last. Very professional and efficient in everything they do…"
Ian, Google review, June 2026
"…ended up coming to my place of work and sorting an old heating system that hadn't worked for years in a car showroom & workshop. Great team of guys"
James, Google review, October 2025
Common questions about what a pressurisation unit does and when it needs attention.
Talk to the pressurisation unit teamNo. A pressurisation unit maintains pressure within a sealed heating circuit by topping up as needed; a circulation pump moves water around that circuit. The two are distinct pieces of equipment, even though they are often installed in the same plant room — see our separate Pump Installations page for circulation pumps.
Frequent top-ups usually point to something else in the circuit — a slow leak, an undersized or failed expansion vessel, or a unit that was never correctly matched to the system. We assess the wider circuit before simply replacing the unit like-for-like.
Yes, where the unit and wider circuit are performing as expected, servicing rather than replacement is often the right approach. We assess this and explain our findings before recommending either option.
We sequence installation and replacement to minimise disruption, and can discuss timing to fit around your operations. The extent of any disruption depends on the specific circuit and installation, which we confirm as part of any survey.
Yes. Pressurisation units, pumps and heating controls often sit on the same circuit, and we coordinate work across all three where a project needs it, rather than treating each in isolation.
It can be. Our commercial boiler servicing and heating maintenance programme can include pressurisation unit checks as part of a planned visit — let us know if you'd like this included when discussing a maintenance arrangement.
Tell us about the circuit, the symptoms you've noticed — such as frequent top-ups or pressure loss — and any access or timescale constraints. We can advise on the right approach and arrange a survey where appropriate.
For an urgent enquiry, please call our office directly.
Current accreditations and registrations.
Message the ComGas office on 01252 214120.