water pump going when the water is hot

[laika]

When the water in the calorifier gets hot, the water pump keeps switching on and off. This may be a recent thing but our habits have changed too: Normally if we're on the water the water pump is off and wouldn't be switched on until after the engine was off and things tidied up. Recently though we've been static liveaboards and I've run the engine whilst parked (and water pump on). I also replaced the immersion heater which never worked with one which does work. Both cause the pump activity.

My first thought was pressure causing a leak, but I've found no trace of one. I've tried dialling down the pressure switch but to eliminate the pump activity I have to pretty much turn it off.

Suggestions?

 

[Jassira]

Your water pump will (should) only come on when the water pressure drops but as your water heats the pressure will increase, so my guess is the pressure relief valve is activating as the temperature/ pressure rises causing the pressure to drop below the "on" pressure of your pump.

 

[RichardS]

Your water pump will (should) only come on when the water pressure drops but as your water heats the pressure will increase, so my guess is the pressure relief valve is activating as the temperature/ pressure rises causing the pressure to drop below the "on" pressure of your pump.

Although Laika says no trace of expelled water is to be seen .... unless the PRV is vented to the outside or back to the water tank?

Richard

 

[laika]

Although Laika says no trace of expelled water is to be seen .... unless the PRV is vented to the outside or back to the water tank?

To be honest I'm not 100% sure where the prv is. I've been sitting down with my copy of Calder to see how things *should* be hooked up (and finally working out what a non-reichian accumulator is for) and when it stops raining will head out for a spot of locker diving to see how it compares with what I've got. A mild problem with the water system is a good thing: I can finally work out how it's glued together....

 

[Yngmar]

If your accumulator is the transparent type (my favorite), you will be able to see the level. So next time the calorifier is cold, mark the level with a pen, then don't use any taps while the calorifier heats the water. Observe accumulator level at regular intervals (before the pump kicks in, obviously). If it is dropping, you got a leak (or PRV venting) somewhere, which is why the pump kicks in. If it is rising, you got backpressure from the expanding water, but that should not trigger the pump.

If it stays the same, something else is going on entirely - is the pump by chance in the vicinity of the calorifier and gets heated up by it?

 

[mattnj]

I had exactly this last weekend....pump ran every 5/10mins when water was hot......turned out to be a ball valve on bottom of calorifier (to drain it) that has a slow (drip drip drip) leak to the bilge.....but only when it was hot....took ages to spot.

 

[nigelmercier]

... working out what a non-reichian accumulator is for ....

Google brings up links about orgasmatrons, so I'm intrigued.

 

[temptress]

When the water in the calorifier gets hot, the water pump keeps switching on and off. This may be a recent thing but our habits have changed too: Normally if we're on the water the water pump is off and wouldn't be switched on until after the engine was off and things tidied up. Recently though we've been static liveaboards and I've run the engine whilst parked (and water pump on). I also replaced the immersion heater which never worked with one which does work. Both cause the pump activity.

My first thought was pressure causing a leak, but I've found no trace of one. I've tried dialling down the pressure switch but to eliminate the pump activity I have to pretty much turn it off.

Suggestions?

I'd say the pressure relief valve is faulty especially if you have only just fixed the immersion heater. My guess would be that the water is heating up more than usual and the pressure build up eventually causes the PRV to dump some water into the bilge activating the water pressure pump to start the cycle all over again.

This can often be fixed by manually working the PRV a few times as they can crud up with scale over time. A new PRV can be had form a plumbers merchants for a well under 10 quid.

 

[laika]

Thanks all. I got distracted by parental care and other duties but will focus on the pressure relief valve when I take everything out of the locker to re-examine the system: all the advice much appreciated

Google brings up links about orgasmatrons, so I'm intrigued.

Personally I'm more of a fan of Steve than Wilhelm but in looking at the black cylinder attached to the pipework I was just going through the possibilities
LDA #&f0 didn't work so not *that* kind of an accumulator
I didn't just miss out on being able to pay "a man" to fix my plumbing forever for a £1 bet because Lucky Lad fell before the line at aintree so not *that* kind of accumulator.
And as for the final kind that I think it wasn't (instead apparently being a device to help maintain *water* pressure)...well I think perhaps that's best explained in song...but not sure that youtube links to the works of Hawkwind are appropriate for PBO....

 

[VicS]

Thanks all. I got distracted by parental care and other duties but will focus on the pressure relief valve when I take everything out of the locker to re-examine the system: all the advice much appreciated



Personally I'm more of a fan of Steve than Wilhelm but in looking at the black cylinder attached to the pipework I was just going through the possibilities

It does seem likely that the expansion and increase in pressure is causing the PRV to lift and that it is not seating again properly thereby allowing the pressure to fall below the pump cut in pressure,

However if the hot water system incorporates a properly sized and set up expansion tank this should absorb the expansion without causing the PRV to lift.

 

[DannyB]

If you are leaking hot water it will evaporate quickly, and may not be obvious.

 

[jwilson]

If you are leaking hot water it will evaporate quickly, and may not be obvious.

Or as in my Jeanneau if it is piped to the bilge sump from the PRV.

 

[RichardS]

If you are leaking hot water it will evaporate quickly, and may not be obvious.

In theory yes .... but at the temperatures under discussion I think that any such effect will be minimal as any leaking hot water will very quickly reduce to ambient.

(Apologies if you're joking and I've taken it seriously )

Richard

 

[gasdave]

When we took over our current boat our first cruise was memorable for our hot water problems - on two occasions I spent well over an hour in the bilges in an uncomfortable position pumping most of a hot water tank's content with a small hand pump. We live and learn!
Our symptoms were very similar to yours and ultimately turned out to be a broken thermostat. The water was dangerously hot:mad-new::hororr: (there'd been quite a lot of motoring) and the PRV kept activating. The leak turned out to be from a fractured pipe on the hot side. The combination, although probably mostly the leak, were responsible for the water pump activation.

 

[jdc]

It does seem likely that the expansion and increase in pressure is causing the PRV to lift and that it is not seating again properly thereby allowing the pressure to fall below the pump cut in pressure,

However if the hot water system incorporates a properly sized and set up expansion tank this should absorb the expansion without causing the PRV to lift.

This diagram (although to be fair, it was pasted to illustrate out how accumulators should be plumbed) misses out a, to my mind vital, element: the thermostatic mixer valve which 'dilutes' the hot water from the tank with cold water before piping it to the taps and shower etc. This could also be the cause of leaks or of the OP's problem.

The water in the tank can get to around 75 to 80 degrees C if from the engine calorifier, which is quite cool for an engine but dangerously hot for a human. It should be reduced to around 45 - 50 C before distribution, and on many yacht systems there is a special mixer to achieve this. See for instance http://www.asap-supplies.com/search/calorifier/hotpot-thermostatic-mixing-valve-520955

 

[RichardS]

This diagram (although to be fair, it was pasted to illustrate out how accumulators should be plumbed) misses out a, to my mind vital, element: the thermostatic mixer valve which 'dilutes' the hot water from the tank with cold water before piping it to the taps and shower etc. This could also be the cause of leaks or of the OP's problem.

The water in the tank can get to around 75 to 80 degrees C if from the engine calorifier, which is quite cool for an engine but dangerously hot for a human. It should be reduced to around 45 - 50 C before distribution, and on many yacht systems there is a special mixer to achieve this. See for instance http://www.asap-supplies.com/search/calorifier/hotpot-thermostatic-mixing-valve-520955

I must say that I'm not aware of ever seeing one of those on a boat although they obviously exist if the part is available.

Richard

 

[VicS]

I must say that I'm not aware of ever seeing one of those on a boat although they obviously exist if the part is available.

Richard

Surecal calorifiers incorporate a thermostatic mixer as standard believe.

Just that the diagram I chose was was C warm system without. A thermostatic blender valve is available as an accessory.

 

[laika]

After a really embarrassingly long period of not using the hot water and not using the water pump (using the foot pump instead) I took everything out from the locker. I believe I identified the prv right at the exit from the tank:

Now annoying thing was that at first it just didn't show the problem. Hoiked out anchors, spare chain, miles of rope, oars, emergency tiller took apart the enclosure for the tank, removed the hose which seems to disappear to an inaccessible part of the bilges, turned on the water, it heated up, no problem. A little later after some washing up the pump starts cycling. And carries on doing it for 4 seconds out of every 20 or thereabouts.

When it's doing it there *is* a slow drip from the prv, but it's a very slow drip, not a trickle. What I have noticed though is the occasional small bubble floating back from the water tank which I'm guessing isn't right. Also having read up a bit more on hot water systems...do I need an expansion tank (not an accumulator, I have one of those)?

 

[VicS]

After a really embarrassingly long period
...........................................

do I need an expansion tank (not an accumulator, I have one of those)?

The purpose of the expansion tank is to absorb the expansion of the water in the hot water system as it heats up so that it does not lift the prv every time.

 

[RAI]

Last time that happened to me it was a bit of plastic on the fresh water pump inlet valve. Water was leaking back from the pressurised side into the tank. I took the unit apart with the intention of replacing both valves (they are a unit) but just cleaning did the job. Jabsco pump.