Maybe a circulating pump?

At the hot water faucet at the greatest distance from this water heater, and also at others, does the water come out hot immediately when you turn it on, or do you have to wait for cold water to pass through first? If immediately, that's what it is.

Unfortunately no hot water :(.. that's why I am taking a look at the heater

How about providing a better-focused picture of the device in question?

I concur the pump is a hot water circulating pump. They are useful for minimizing the wait time for hot water (and the quantity of water wasted down the drain) waiting for hot water to arrive at fixtures located far from the hot water heater. In my experience circulating pumps have a life expectancy of 5 +/- years, but the temperature and water quality could affect that.

In my experience circulating pumps will easily last decades because of the way they are designed even under harsh operating conditions. Even if the pump wasn't working or turned off the water heater would still work so It is not your problem.

You have a gas water heater so the problem is in the gas valve or flame proofing assembly and most likely the thermocouple or igniter.

Agree you should still have hot water if the pump is off--it will just take longer to get there.

In our area, I find that it's the plastic impellers that die in 5 +/- years. The pumps are relatively inexpensive $400 +/- and it's less expensive to replace them than it is to pay a $90/hr plumber plus a $100 service call charge to replace a $150 impeller cartridge.

If you're talking about cheap rebranded Chinese junk pumps on the market from $50 to $100 then I'll agree with you concerning longevity and durability. You get what you pay for and cheap pumps won't last long.

What I'm talking about are the quality pumps that will last decades. This UPS20-42 Grundfos pump I have here was made in the late 70's with brass composite bearings and shaft with a stainless steel impeller. This pump snapped a shaft because the water froze, but would probably still be running today otherwise. The present equivalent Grundos replacement UPS15-42 costs $160 with a stainless steel impeller and well under the $400 you quoted for a cheap pump so there are many good pumps well under 4 bills that will last decades. (the impeller is the shiny thing in the bottom of the picture)

I can't make out the type code on the OP's Grundfos pump but they make good pumps and will easily outlive the life of that water heater, just don't let them freeze. If your experience comes from the homes you built, and thinking a cheap pump only lasts 5 yrs and costs $400 then your Plumber sub was putting the screws to you, sorry to here.

Kevin,

I grew up on a farm and started working on pumps as a teenager. That was a long time ago. They don't make 'em like they used to. The Grunfos pumps designed for hot water circulation have plastic impellers. You can purchase one with an integral timer for around $350. These are lower cost and quality than pumps used in hydronic heating applications.

Tim, so the picture of the stainless steel impeller must be fake, even if I did pull it from a grundfos pump used on a thermal solar collector and I just took the picture. The data for select grundfos pumps for hot water circulation state stainless steel impellers, is this information fake too?

Just admit you made a mistake on the price of pumps and the material used for the impellers because none have plastic impellers. The composite impellers they do use are made from glass fiber reinforced Polyethersulfone with the rockwell hardness of steel and a tensile strength around 18,000 psi., and twice as the strength of the strongest plastic, Polycarbonate.

@kevin9408,

I didn't claim your picture was a fake. I shared my experience with hot water circulator pumps of the type commonly installed today. Like most manufactured things, the construction of hot water circulator pumps is different from 40 or 50 years ago driven by the need to keep costs down. You can certainly choose a more expensive variety and the longevity may be better, too.

With regard to polysulfones they are polymers. We typically refer to polymers as "plastics." More specifically, polysulfones are thermoplastics, and yes, in many applications they are glass reinforced to improve their performance.

My plumber charges $400 for a replacement hot water circulator pump, but if you want to tackle the replacement on a DIY basis, here's a link to a source where you can pick one up for around $350 https://www.supplyhouse.com/Grundfos-595916-UP15-10SU7P-TLC-Comfort-Hot-Water-Recirculation-Pump-3-4-NPT-115-V?utm_source=google_ad&utm_medium=shopping_neutral&utm_campaign=Shopping_Neutral_MPLTV&gclid=EAIaIQobChMIxtyd06Wt-gIVlMDICh1F7A_nEAQYASABEgKSI_D_BwE

ETA: I should have also included a link for the impeller cartridge. It's only $130 including tax from this source, not the $150 I had in my core memory

https://www.supplyhouse.com/Grundfos-506176-Cartridge-for-UP15-10-Series?utm_source=google_ad&utm_medium=Shopping_ntm&utm_campaign=Shopping_NTM_New_users&gclid=EAIaIQobChMI3uKoh4au-gIVyVByCh0rbwk8EAQYBSABEgJKQfD_BwE

The amber-colored component is the pump's impeller. It's an injection-molded thermoplastic part.

@kevin9408,

Just following up to see if you had any questions about polysulfones or thermoplastics in general. It's been over 40 years since my last course work in polymer science, but we had polysulfones back then and the fundamentals don't change.

With regard to physical properties of polymers under consideration for a hot water circulator pump impeller, I wouldn't focus on hardness nor tensile strength. What is more important is their thermal stability, distortion temperature, their ease of use in injection molding applications, and their chemical resistance in the expected range of pH and concentration of chemicals either naturally occurring or used in water treatment.

odd, my mind drifted off to the subject of dishwater reading the last two posts. Tim, I always dismantle bad centrifugal pumps if the problem wasn't a bad motor winding and never found any closed impeller made with PES+GF30 broken. With general purpose ABS, PVC, LDPE impellers it happens.

PES is the top performer of any amorphous polymer with excellent resistance to impact loads, fatigue or erosion and extremely unlikely they would break in a Grundflos or any brand pump. You'd need to go to a semi crystalline polymer high performance polymer such as PEEK to hold up better.

When I see you reference "plumber" could your mind also drift to dishwater listening to the "plumbers" explanation as to the reason of failure? Or your memory has become a little foggy over time,on this and what you learned over 40 years ago? E. FUDD syndrome maybe?

I have and presently use many types of pumps and rebuild pumps I find. I've never seen even a general purpose polymer impeller break, but have eroded and lost tolerance dropping head to an unusable level. Even the cheapest pond pumps don't break an impeller. and erode or bushing wear out. Based on my experience I'm going to give you a Pinocchio here.

The pump you linked to has very low tolerance to operate while the thermal bypass valve is closed until the timer turns it off. It's inefficient by design and maintains a high load on the motor so any failure would most likely be electrical, or worn out rotor bushing bearings in the cartridge causing poor or no performance. The latter is what I see in most pumps that still run. There aren't a lot of reviews for the cartridge suggesting it's not often purchased. Maybe your plumber should have a few cartridges in the truck if the impeller breaks instead of replacing the entire unit, it would be cheaper and quicker.

Good to know that Grundfos pumps are, in fact available with plastic impellers, if you'll forgive the use of the vernacular.

The problem with changing out a $130 cartridge on a $350 pump is the potential for the timer or some other part to go long before the new cartridge dies. Then the client has wasted the cost of the cartridge, service call and the hourly rate which is pretty close to the cost of a replacement pump less the plumber's mark up on it. For someone with DIY skills installing a replacement cartridge is a good Saturday morning project. Most of my clients are either too busy or not capable of doing it or don't want to be supervised by their spouse while they attempt it.