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Mark Downing

Mark Downing

Founder / Service Specialist

Rating

Reviews

LICENSES: MASTER PLUMBER, GAS SERVICE

Mark started GSMS in 1987 with a single van and a commitment to doing things the right way. While he has transitioned the company to the second generation, Mark’s passion for the trade keeps him in the field every day. You’ll still find him visiting clients, sharing his 40 years of expertise, and ensuring the Downing standard is met on every call.

Name: Mark Downing

Recent Jobs and Reviews

Rated 4.9 out of 5 stars based on 133 customer reviews

Customers say: The overall sentiment across these reviews is overwhelmingly positive, reflecting high levels of customer satisfaction and appreciation. Customers consistently express enthusiasm about the quality of service they received, with recurring praise for professionalism, expertise, and efficiency. A dominant theme throughout is the technical skill and knowledge demonstrated by the service team, with many reviewers highlighting how thoroughly problems were diagnosed and resolved. The interpersonal qualities of the technicians emerge as another strong positive trend, with customers frequently describing them as friendly, personable, pleasant, and respectful. Communication stands out as a particularly valued aspect, with reviewers appreciating clear explanations, patience in answering questions, and being kept informed throughout the service process. Timeliness and punctuality are consistently mentioned as strengths, alongside respect for customers' property and maintaining clean, orderly work practices. Many customers express strong loyalty and trust in the company, with several indicating they are repeat customers or plan to continue using the service. The tone is enthusiastic and grateful, with multiple reviewers offering strong recommendations and expressing genuine happiness with the results. Overall, these reviews paint a picture of a service provider that excels in both technical competence and customer care, creating consistently positive experiences that foster long-term customer relationships.

At a glance

GSMS Air•Heating•Plumbing has completed 25 jobs between August 2026 and September 2026.

The 15 customer reviews shown here average 4.8 out of 5.

The most recent job was on September 22, 2026.

Recent work covers Merrimack, NH, Nashua, NH, Manchester, NH, Bedford, NH and Amherst, NH.

Job Locations and Reviews

Remove toilet and reset
Remove toilet and reset
Mark D.
Mark D. Checked in
Remove toilet and reset
Amherst, NH 03031
Review
Mark is careful, thorough, and has very helpful suggestions.
Sharon - Merrimack, NH 03054
Merrimack, NH - This proposal covers the complete removal of your existing standard bathtub and the professional installation of a premium Walk-In Therapy Tub. To ensure this new therapeutic tub fills quickly and operates flawlessly, we will be heavily upgrading the underlying plumbing to 3/4" lines and running new dedicated electrical circuits to power the jets and inline heater. We will also be coordinating with our trusted partner, Scott, to handle the final tile, drywall, and paint restoration once the plumbing installation is complete.

Scope of Work

1. Demolition & Area Preparation

Tear-Out: We will carefully disconnect and remove the existing bathtub and immediate wall surrounds.

Debris Removal: All old tub materials and job site demolition debris will be hauled away and properly disposed of.

Area Prep: We will prep the exposed floor and framing to securely accept the new, heavier walk-in tub unit.

2. Plumbing Rough-In & Upgrades

Water Line Upsizing: Walk-in tubs require high water volume
Mark D.
Mark D. Checked in
This proposal covers the complete removal of your existing standard bathtub and the professional installation of a premium Walk-In Therapy Tub. To ensure this new therapeutic tub fills quickly and operates flawlessly, we will be heavily upgrading the underlying plumbing to 3/4" lines and running new dedicated electrical circuits to power the jets and inline heater. We will also be coordinating with our trusted partner, Scott, to handle the final tile, drywall, and paint restoration once the plumbing installation is complete. Scope of Work 1. Demolition & Area Preparation Tear-Out: We will carefully disconnect and remove the existing bathtub and immediate wall surrounds. Debris Removal: All old tub materials and job site demolition debris will be hauled away and properly disposed of. Area Prep: We will prep the exposed floor and framing to securely accept the new, heavier walk-in tub unit. 2. Plumbing Rough-In & Upgrades Water Line Upsizing: Walk-in tubs require high water volume
Merrimack, NH 03054
Review
Great service as always. Thank you so very much for squeezing us in! We are very grateful.
Ray & Di - Manchester, NH 03102
Mark D.
Mark D. Checked in
Set toilet
Manchester, NH 03102
Mark D.
Mark D. Checked in
.install faucet
Londonderry, NH 03053
Mark D.
Mark D. Checked in
Installed taco leak shut off
Amherst, NH 03031
Look at boiler and mini spilts.Will send estimates by email
Look at boiler and mini spilts.Will send estimates by email
Mark D.
Mark D. Checked in
Look at boiler and mini spilts.Will send estimates by email
Goffstown, NH 03045
Mark D.
Mark D. Checked in
Replacement of failed macerator toilet system with a new Liberty system. Includes new toilet and pumping system. Existing connections must be rated for new unit and have proper venting per building code.
Londonderry, NH 03053
Mark D.
Mark D. Checked in
Replaced drain for water equipment. Preventactive maintenance on all heating equipment as well as both thankless water heaters. The boiler in the barn needs a bee low water cut off sensor as it did not deactivate the burner when the test button was pressed. I also noticed the condensation trap to be full of silver metallic particles which indicates the heat exchanger is deteriorating internally. The boiler was left shut off with a red tag as a safeguard.
Moultonborough, NH 03254
Mark D.
Mark D. Checked in
Replace tub and shower valve
Merrimack, NH 03054
Replace laundry sink and faucet in garage
Replace laundry sink and faucet in garage
Mark D.
Mark D. Checked in
Replace laundry sink and faucet in garage
Sandown, NH 03873
Mark D.
Mark D. Checked in
Replaced garbage disposal
Nashua, NH 03060
Mark D.
Mark D. Checked in
Replaced expansion tank and relief valve
Barrington, NH 03825
Mark D.
Mark D. Checked in
Check toilets,looks like there be a blockage in vent by roof.Will call back when are snake with camera comes in.We can remove 3 floor toilet and run snake with camera through line to locate blockage
Bedford, NH 03110
Mark D.
Mark D. Checked in
Sent estimate
Wilton, NH 03086
Found drain from water softener outside of drain pipe, pressure on back wash must have blow it out of the drain pipe.Install hangers on the drain line
Found drain from water softener outside of drain pipe, pressure on back wash must have blow it out of the drain pipe.Install hangers on the drain line
Mark D.
Mark D. Checked in
Found drain from water softener outside of drain pipe, pressure on back wash must have blow it out of the drain pipe.Install hangers on the drain line
Moultonborough, NH 03254
Mark D.
Mark D. Checked in
This proposal outlines the plumbing labor and materials required to add a functional utility sink setup to your basement utility boiler room. To avoid the massive mess, expense, and concrete jackhammering associated with traditional basement plumbing, we will utilize a premium macerator pump system. This advanced technology grinds and pumps the waste upward, allowing us to safely tie your new basement fixtures directly into the home's existing overhead main waste line. Scope of Work Waste Discharge: We will route a 1-inch PVC discharge line from the powerful macerator pump, running it up and tying it safely and securely into your home's main overhead waste line. 2. Utility Sink & Water Lines The Sink: We will supply and install a heavy-duty Mustee 20-inch utility sink, equipped with a reliable basic chrome faucet. Drainage: The utility sink will be piped to drain directly into the Saniflo macerator pump, utilizing the pump to efficiently eject the sink's greywater. Water Supply:
Nashua, NH 03064
Mark D.
Mark D. Checked in
This proposal outlines the replacement of your failed 40-gallon Bradford White power-vented natural gas water heater. Because your tank is currently covered under the manufacturer's warranty, the physical cost of the new tank itself is covered. The pricing in this proposal strictly covers the professional labor, the distributor's warranty processing fee, the necessary structural plumbing modifications, and the required safety code upgrades to properly install the new unit. Scope of Work 1. Demolition & Warranty Processing Removal: We will safely drain, disconnect, and remove your existing failed water heater. Warranty Handling: GSMS will handle the logistics of returning the failed tank and will cover the $100 warranty processing fee charged by the distributor on your behalf. 2. Equipment Installation & Code Upgrades The New Tank: We will supply and install your new warranty-replacement 40-gallon Bradford White power-vented natural gas water heater in the exact same footprint. Conn
Amherst, NH 03031
Review
CALL BACK IS IN THE WORKS- THERMOSTAT IS BLACK - NO REPSOPONSE.
Montcalm - Nashua, NH 03060
Mark D.
Mark D. Checked in
Found overflow switch off.Looks like air was blowing on it from door cover moved switch .
Nashua, NH 03060
Mark D.
Mark D. Checked in
Removing vent and relocate drain line under sink and install atm vent.We will do temperaily cap on roof flange.Home owner to do have roofer do permanent patch.Will cut vent pipe and leave inside wall unless owner has sheetrock removed than we can remove pipe.
Manchester, NH 03102
Outdoor unit making noise.Checked amp, capacitor and charge everything is fine.outdoor coil is in bad shape.By listening to recording it sounds like bearings are wearing out causing noise
Outdoor unit making noise.Checked amp, capacitor and charge everything is fine.outdoor coil is in bad shape.By listening to recording it sounds like bearings are wearing out causing noise
Mark D.
Mark D. Checked in
Outdoor unit making noise.Checked amp, capacitor and charge everything is fine.outdoor coil is in bad shape.By listening to recording it sounds like bearings are wearing out causing noise
Merrimack, NH 03054
Mark D.
Mark D. Checked in
Replaced sprayer under warranty
Newmarket, NH 03857
Look at shower for water leak,found water leaking through left front floor tile were caulking was missing.Looked at master bathroom toilet and gave estimate to repair or replace toilet
Look at shower for water leak,found water leaking through left front floor tile were caulking was missing.Looked at master bathroom toilet and gave estimate to repair or replace toilet
Mark D.
Mark D. Checked in
Look at shower for water leak,found water leaking through left front floor tile were caulking was missing.Looked at master bathroom toilet and gave estimate to repair or replace toilet
Manchester, NH 03102
Mark D.
Mark D. Checked in
Had to remove heat exchanger and blow out with nitrogen.Also cleaned top heat exchanger.
Barrington, NH 03825
Mark D.
Mark D. Checked in
Sent Estimates
Sandown, NH 03873
Bedford, NH - Replaced fill valve and clean toilet handle
Mark D.
Mark D. Checked in
Replaced fill valve and clean toilet handle
Bedford, NH 03110
Review
Extremely professional and on time, great work! Highly recommend their services.
Georgine - Bedford, NH 03110
Review
As always very professional
Steve - Nashua, NH 03064
Review
Mark and his team came in install my new kitchen appliances. I switched from gas to induction for my stove, replaced my over the oven microwave and replaced my refrigerator so they installed my water line so now I have an ice maker!
Terry - Manchester, NH 03109
Review
Totally fixed my problem in short time. Always do neat as well
Sandra - Bedford, NH 03110
Review
Mark was very professional, found an issue with the system, fixed it.
Craig - Madbury, NH 03823
Review
Exceptional service
Paul - Nashua, NH 03062
Review
I had a need to replace the shutoff valve from the main water supply to the building per the water utilities company. Mark worked with the water utilities company to coordinate the work that needed to be done and installed a new shutoff valve.
LoriB - Milford, NH 03055
Review
Issues resolved quickly and efficiently
Mark - York, ME 03909
Review
Great work and kept me informed the entire time. Did a great job, fast, clean, and customer-focused. Highly recommend.
Gregory - Auburn, NH 03032
Review
Mark was on time (on the early side of the timeframe) and throughly checked out the ac and plumbing. Pleasant demeanor and went over everything he did and gave the systems a good bill of health.
Nelson - Merrimack, NH 03054
Review
Excellent service!
Sharon - Merrimack, NH 03054
Review
Friendly, thorough and efficient!
Bob - Sandown, NH 03873
Trusted Quality & Service