Water pump running continuously, but . . .

[LittleSister]

Ok, I've read various other posts on the topic, and it seems this can be caused by pretty much anything that could possibly go wrong with a pumped water system, but I'm very much up against it, and my specific symptoms may enable the cognoscenti to home in on the actual (or at least most likely) cause of my problem, rather than just throw up random possibilities.

When turned on, the pump runs as normal (as if one had run a tap) for a few moments, then instead of turning off, suddenly slows to perhaps half(?) speed and keeps going like that.

I recently had the calorifier pressure valve fail. It may have been (I can't now be certain) that the pump was then running continuously at 'normal' high speed, and not 'stepping down' as it now is .

As fixing the calorifier is an ongoing, and very frustrating, saga, I have now cut that out the the system and have only the cold side of the system connected.

I found a small leak from the outlet of the water pump, and assumed that was the problem, but that is now fixed and there is no change. Inhale searched the rest of the system (as far as is visible) and haven't found further leaks.

Over to you!

 

[mrangry]

I had this issue with an old par max pump and it was the micro switch which was faulty. I replaced the micro switch and it worked for a short time but ended up just replacing the pump and realised how efficient and quiet a modern replacement pump could be.

Was the calorifier pressure relief valve faulty, or was the system running at higher that normal pressure?

 

[Sticky Fingers]

Empty tank causes this.

 

[LittleSister]

Empty tank causes this.

The tank is almost full, and there's plenty of water coming out of the (cold only) taps when I turn them on.

I had this issue with an old par max pump and it was the micro switch which was faulty. I replaced the micro switch and it worked for a short time but ended up just replacing the pump and realised how efficient and quiet a modern replacement pump could be.

Was the calorifier pressure relief valve faulty, or was the system running at higher that normal pressure?

If the micro-switch was faulty, wouldn't this fail to either turn on or turn off the pump, rather than have it run ay half-ish speed after a few moments? On the other hand, if it was failing to turn off, perhaps it is running at full pelt while it is pumping water along until it reaches normal pressure, then running more slowly as the motor is spinning in stationary water that has nowhere to flow?

 

[LittleSister]

Was the calorifier pressure relief valve faulty, or was the system running at higher that normal pressure?

There's an idea! (I missed this on first reading, in a rush.) An appealing one, too. Getting the old valve out is proving very challenging and very time consuming.

In my experience having two different, seemingly unrelated problems at once is often actually two symptoms of the same underlying problem once I finally see the connection (or, they're actually genuinely unrelated and coincidental ).

 

[Momac]

I had a few water pump issues usually at this time of year after the long winter idle period.
I recently opened up the pump and found limescale grit inside . Also found grit in the pump intake strainer .
Cleaning the grit out restored pump performance.

In the past I have found corroded electrical contacts on the pressure switch , a sticking pressure switch that responded to being cleaned and operated manually a few times .
I think a sticking pressure switch is worth investigating . As you have temporarily taken out the hot water circuit it is perhaps not surprising if the pressure switch needs adjustment .

 

[MoodySabre]

Check that the breather isn’t blocked. The initial burst may be creating a partial vacuum.

 

[Chris CJ]

If you have an accumulator cylinder , has the pressure been checked , ours failed giving similar symptoms. The internal rubber bellows had failed (20 years old ) , replaced , problem resolved.

 

[Boater Sam]

The microswitch in the pump is failed closed and the over pressure has opened the PRV. Now you have no PRV, the pressure is very high and the pump is stalling due to the high loading. Something is going to burst soon, possibly the calorifier.
Stop using it immediately.

 

[snowbird30ds]

Could just be the valves in the pump leaking back allowing the water pressure to escape back to the tank.
A pressure gauge on the outlet would make diagnosing much easier.

 

[LittleSister]

Thanks for the suggestions.

So, last night I had become convinced it was likely the pump micro-switch had failed, as MrAngry had suggested. Researched how to fix it, and now have to go back to boat to check whether the switch assembly looks like the current (arf, arf!) Jabsco replacement switch. (I suspect the pump is an earlier model - the model name and number (but not the manufacturer's logo) have washed off both this and the accumulator - and I will have to buy a complete new pump .)

This is all a complete distraction from other very urgent boat (and other) tasks, so I am stressed and pressed for time. Access to the various parts is poor.

My current thinking on the various latest suggestions today (I reserve the right to change my mind later ):

Limescale grit in pump:- quite possible but can't think how this fits the symptoms. For now will check the strainer, but not dismantle the pump.

Taking hot water system out is raising the pressure: - I can't see how (simple system - just two taps each hot and cold).

Blocked breather:- tank lid is currently loose, so no vacuum there.

Accumulator has failed:- possibly, I currently have no means of checking the pressure.

Microswitch has failed and has opened PRV, risk of bursting calorifier:- failed microswitch is my current prime suspect, but no risk of calorifier busting as supply to it is now cut off (and when it wasn't PRV was leaking any pressure). If the pressure in cold sytem is too high it is not by much, as the flow from the cold taps does not seem noticeably different from normal.

Valves in pump leaking:- I'm not sure this would result in the 'two-stage' pump speed reported.

A pressure gauge on output would aid diagnosis:- It certainly would, but I don't currently have a means of connecting a pressure gauge to the 1/2" system. p.s. I have belatedly discovered there should be a Schrader valve on the top of the accumulator, so once I have researched what the pressure should be I will check that out.

 

[LittleSister]

Update - I have ordered a new pump, so that should eliminate the switch, pump diaphragm failure, grit contamination, etc. I could do without the cost, but the switch alone (if available) was a third of that (and I could spend the difference on fuel to get to and from the boat repeatedly), and at worst I will have a spare pump.