How to Prime a Grundfos Pump: Step-by-Step Instructions for Homeowners

 If your pump is running but the tap is still dry, switch it off before checking whether it needs priming. The pump chamber needs water before startup, and the filling method depends on the model and water supply. 

Today, we'll walk you through the whole process of how to prime a Grundfos pump with separate SCALA2 and CMBE steps. If you have a Grundfos pump for home use, we’ll also show you how to check that it’s supplying water properly.

TL;DR

• Find your model and product number, then follow its matching manual.
• Isolate power and release pressure before opening any filling point.
• For SCALA2, fill the housing with at least 0.45 U.S. gallons (1.7 liters), then hand-tighten the plug.
• For CMBE, use supply pressure or manual filling as your model’s manual directs before startup.
• Vent air through an open tap and confirm steady delivery. Stop if water fails to arrive.
• Check valves, suction leaks, intake submergence, restrictions, and permitted lift if priming fails.
• Circulators need system bleeding.
• Leave electrical and internal repairs to qualified technicians
• Ask 24hr Supply about replacements after diagnosis.

Which Grundfos Pump Are You Priming?

You can identify your pump by checking the model and product number on its nameplate. Use those details to find the matching manual, and check that its voltage matches your unit. Grundfos pump models can look similar, so appearance alone won’t tell you which instructions to follow.

If you’re unsure what kind of booster you have, our comparison of different types of booster pumps gives you some background.

Here’s what each pump type is used for and which instructions apply to yours.

P.S. If you’re identifying a Grundfos pump in a heating system, our Grundfos circulator pumps category can help you compare models. For those units, continue with the system’s bleeding instructions.

How to Prime a Grundfos Pump Step by Step

Once you’ve identified the unit, keep its manual beside you and check how water reaches the inlet. A pressurized supply can fill a pump differently from a line that draws water upward. 

Here are the procedures for the two booster systems.

Prime a Grundfos SCALA2 Pressure Booster

For your SCALA2 Grundfos pump, follow the startup sequence in Grundfos’s SCALA2 instructions . 

Our Grundfos SCALA2 pressure booster listing uses product number 93013251 , so compare that number with your own unit’s label before you begin.

1. Shut Off Power and Release Pressure

Before opening the pump, unplug it or isolate its power supply and prevent an accidental restart. For an existing pressurized setup, isolate the water feed as needed and open an outlet tap to release pressure. 

Let hot components cool, and leave wiring work to a qualified person.

2. Identify the Fill Point

Check that your water source is available, then locate the priming plug shown in your manual. The drain plug serves a different purpose, so check the diagram before removing anything. A clean funnel and clean water will help you fill the housing.

3. Fill the Pump Housing

With power isolated and pressure released, remove the priming plug. Grundfos specifies at least 0.45 U.S. gallons, or 1.7 liters , of water before the first startup. Its self-priming feature still needs this initial fill, so pour the water into the pump housing through the priming opening. Keep it out of the pressure tank, which has a separate function.

Check here to see how to install a Grundfos SCALA2:

4. Refit the Plug by Hand

Once the housing is filled, put the priming plug back in place. Grundfos instructs you to tighten it by hand.

5. Start With a Tap Open

Reopen any supply valve isolated during preparation, and open a tap for venting before restoring power. When water flows without air, close that tap. Then open the highest tapping point, preferably a shower, and adjust the pressure using the controls described in the manual.

6. Check Actual Delivery

After adjustment, close the tapping point, then check normal operation at an outlet. You want sustained water delivery without abnormal leaks or operation. 

Motor noise alone does not confirm success. If water fails to arrive or an alarm returns, stop and use the troubleshooting checks below.

Prime a CMBE Booster System

For the CMBE-1-44, first check how water reaches the inlet. Grundfos gives separate startup instructions for a pressurized supply and a suction setup in its CMBE 60 Hz North America manual . 

Before starting, check the pressure tank’s precharge against the manual’s requirement. You’ll also need to follow its flushing instructions if the drinking-water system is new or has been unused for a long time.

1. Prepare the Unit Safely

Isolate power and release pressure before opening a fill point. For your Grundfos pump installation, check the inlet arrangement against the manual. 

The water-flow arrow shows Grundfos pump flow direction from inlet to outlet. A motor-rotation arrow refers to shaft movement.

2. Use Supply Pressure Where Available

If the inlet has positive pressure, Grundfos directs you to open the inlet and outlet valves, then open an outlet tap so water passes through the pump.

3. Fill Manually Where Required

For flooded-suction or suction-lift setups, locate the vent plug on the front above the inlet. The manual specifies a 10-mm Allen wrench. Remove the plug and fill through the port with a funnel until the pump accepts no more water. 

Air escapes through the open port. Check the accompanying CM/CME instructions for inlet-pipe filling requirements and permitted suction arrangements.

4. Close the Fill Point and Start

If you filled the pump manually, refit the vent plug without cross-threading. For either inlet arrangement, make sure the inlet and outlet valves are open, then restore power and use the Start/Stop control.

5. Confirm Flow Before Adjusting Pressure

Check for sustained water delivery at an open outlet, then adjust pressure within the installation’s operating limits. If inlet water is unavailable or delivery fails, stop and investigate the cause before restarting.

Why Won’t Your Grundfos Pump Prime?

Your pump may fail to prime because water drains away, air enters the suction line, or the inlet cannot supply enough water. The useful clue is what happens after filling, so note the symptom before trying again. 

Here are the checks we’d start with.

Grundfos notes that SCALA2 may need priming more than once when suction depth exceeds 20 feet, or 6 meters . Follow its model-specific instructions and keep the housing supplied with water. Repeated dry running can damage the pump.

If these checks don’t resolve your Grundfos pump problems, stop before dismantling the unit.

Pro Tip: Check out our Grundfos pump troubleshooting guide to help you find out why your pump won’t prime.

Who Sells Grundfos Pumps Near Me?

You can buy Grundfos pumps through our online store and check delivery estimates for your ZIP code on the product page.

If a diagnosis confirms that you need a replacement, browse our Grundfos booster pumps . The replacement should match your water source and pressure needs, and you should check its voltage and connections before ordering.

Contact us today with your pump’s model number and water-source details. We’ll help you compare replacement options and check which specifications match your setup before you order.

FAQs

Are Grundfos Pumps Self-Priming?

SCALA2 and some other models are self-priming. They can remove air from the suction line after the required initial fill. Check your model’s manual to confirm.

How Do I Bleed a Grundfos Pump?

For a heating circulator, use the system’s designated air vents and follow its instructions. Avoid opening an unidentified plug on a hot, pressurized system because it can release scalding water.

What Are Common Problems With Grundfos Pumps?

Common issues include electrical control faults, worn parts, and casing or seal leaks. Grundfos pump repairs need a qualified assessment. Our guide to common booster pump problems and fixes explains what to check.

Can I Repair a Grundfos Pump Myself?

You can do the owner checks listed in your manual. Leave electrical or internal Grundfos pump repair to a qualified technician, and confirm the fault before ordering Grundfos pump parts. A confirmed diagnosis helps you decide whether to repair Grundfos pump components or replace the unit.