Specific or complex project ahead? Get in touch for a free, fast quote.
Stuart Turner Mainsboost MJ3 HM Booster Pump | 41729 | 3.5 Ba
Regular price
$1,250.00
Inc. VAT
$1,041.67
Exc. VAT
FREE Express Delivery (1-3 days) in UK Mainland on most orders*
Excluding: Solar Panels (£170 delivery / free above £2,500), Batteries (£39 delivery), Small Items (£4.95/5.95 delivery / free above £500)
Contact Us to check for Next Working Day Delivery or Same-day Delivery options
Contact Us for Click & Collect options
Custom quote available on request
*See checkout or shipping policy for full details
Payment options
Tools & Kits
Build your kit
Need a full system?
Design your complete solution in minutes with our kit builders.
Do you have a question
about this product?
One of our expert advisors will be happy to help you!
Contact Us
The Stuart Turner Mainsboost Charger MJ3 HM (41729) is a horizontal vessel-mounted mains water booster pump that bolts directly onto a Mainsboost 200SH or 250SH steel horizontal pressure vessel. It lifts weak incoming mains supplies by up to 3.5 bar, delivering stored, potable cold water at consistent pressure to showers, taps and appliances across a home or small commercial property.
Because the pump sits on top of a horizontally mounted vessel, the whole system has a low overall height of roughly 815 to 835 mm, making it the right choice for lofts, under-stairs spaces, utility rooms and restricted-headroom plant areas where a tall vertical vessel will not fit. It is WRAS approved, built around a brass peripheral pump with dry-run protection, and backed by a 5 year manufacturer guarantee.
3.5 bar
Pressure boost
4.3 bar
Max head (43 m)
From 50 dB(A)
Typical noise level
398 W
230 V, 1.8 A full load
WRAS
Approval 1501305
5 years
Manufacturer guarantee
What is supplied
This listing is for the MJ3 HM pump unit only, supplied with its mounting bracket, manifold assembly with 22 mm bypass and integral non-return valve, two 240 mm flexible hoses and a pre-wired 1.5 m supply cord. The Mainsboost 200SH or 250SH horizontal vessel and the upstream line-in kit (Monobloc for 22/28 mm, or the 35/42/54 mm kit) are separate items and must be ordered to complete the system.
Compatibility: horizontal vessels only
The MJ3 HM is designed for the Mainsboost MB 200SH and MB 250SH horizontal steel vessels only. For vertical vessels (100 to 450 litre), the MJ3 VM (41712) is the correct pump. The two are not interchangeable.
Electrical and installation safety
Installation must be carried out by qualified persons in line with current water regulations and BS 7671. The pump must be connected via a dedicated double-pole switched fused spur with a 3 A fuse, and a 30 mA RCD should protect the supply circuit. The motor casing can become very hot in normal operation, so it must be sited where it cannot be touched. Cold water use only, 4 to 35 degrees C.
Key features
Direct on-mains boosting
Takes water from the rising main and stores it in a sealed diaphragm vessel, so supply to outlets is balanced and consistent even when mains flow is poor.
Green energy bypass
A 22 mm bypass with integral non-return valve lets extra mains flow fill the vessel directly. Leave it open above 12 l/min incoming flow, close it below 12 l/min for best pump efficiency.
Programmable controller
Digital pressure control with adjustable set point, differential, low and high pressure trips and pump run timer. Factory preset to 3 bar set point with an alarm buzzer and fault display.
Space-saving horizontal layout
Mounts on the 200 or 250 litre horizontal vessel for a low profile, ideal where headroom is restricted or a tall vertical vessel simply will not fit.
Robust, protected pump
Brass pump body and brass impeller with an EPDM / PTFE / aluminium oxide mechanical seal, dry-run protection and an auto-reset thermal trip on a continuous-duty (S1) induction motor.
Quiet and approved
Typical noise from 50 dB(A), never above 70 dB(A) at 1 m. An optional sound attenuation cover reduces noise by up to 15 dB(A). WRAS approved and CE compliant for potable water.
Where it works best
Designed for single-occupancy homes with low mains pressure, where the vessel and pump can sit in a utility room, cupboard or loft, and for multiple-occupancy buildings where each apartment has its own vessel and pump behind a shared upstream line-in kit. For high-demand properties, additional Mainsboost vessels can be connected in parallel. The system is also suited to installations with a water softener, which must be included in the same pipe run.
Technical specification
System dimensions with Mainsboost horizontal vessels
Check clearances before you order
Overall system height is quoted differently across Stuart Turner literature revisions (from about 795 mm up to 888 mm). The dimensions above are from the latest installation manual. Allow extra clearance above and around the pump for cooling, hose routing and servicing access, and confirm against the vessel and bracket you receive.
Installation and commissioning notes
Fix the vessel on its two mounting cradles, spaced as far apart as possible within the weld seams, then fit the pump bracket and connect the two flexible hoses, which must be used to isolate the pump from pipework forces. The vessel is delivered pre-charged to about 1.4 bar and the charge should be set against the static mains pressure using the schrader valve with the vessel empty. Fit a drain port between the isolation valve and the vessel, remove flux residues before the pump is connected, and prime the pump before starting to protect the shaft seal. Locate the unit dry, frost-free and easily accessible, with the floor or support able to carry the vessel full of water.
Frequently asked questions
BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
Tools & Kits
Build your kit
Need a full system?
Design your complete solution in minutes with our kit builders.
Do you have a question
about this product?
One of our expert advisors will be happy to help you!
Contact Us