356 Water Heater Fluctuates Hot and Cold

[CharlieSea]

Either from the engine or the electric water, the water goes hot and cold when turned on. It takes a while to go warm or hot and then quickly goes to cold then back after a while. Does anyone have any ideas why I can't get a constant stream of hot water?

 

[jviss]

When it fluctuates, is it nice and hot immediately after it turns from cold? A sense of the timeframe of your experience would be helpful.

 

[seadaddler]

Check the screens on the hose fitting at the water heater tank,
Mine were clogged cutting down hot water.
It’s just an idea
Nick

 

[Gene S]

Yes, screens. Do you have a mixing valve at the tank? Mine varies when the pressure pump comes on.

 

[Ron20324]

Did you get the manual which would tell you how to burp it? PROBABLY open the safety valve

 

[Benny17441]

You must be using a mixer valve and the water pressure is fluctuating in one of the lines. Can usually happen when there is air in one of the lines or air trapped in the hot water tank. Check the lines for leaks (water out/air in).

 

[richard9525]

I believe the water tanks have thermostats.Is that a possibility.

 

[chuckwayne]

only the electric side has a thermostat; the engine driven just circulates cooling water. I agree with the air in the lines theory, they may need to be bled/burped. If the PO installed a tempering valve, air in the lines could cause what you're getting.
We've never had this issue in Escape

 

[Jerry Clark H356 SV Persi]

Never had this issue on Persistence either.

 

[CharlieSea]

Thanks for all the replies. Seems like burping is the answer. Will try tomorrow and let you know.

 

[CharlieSea]

It took a while to figure out that there's hot water until the pump comes on then it goes warm/cool/sometimes cold. Then it can get hot again. 'Hadn't put 2 and 2 together until rereading Gene's post. Unfortunately, thought it was due to a 15 year old water heater; a plumber friend said the cold water internal down spout had probably broken off and the cold water was rushing in. Also the SeaWard factory said the life expectanscy was 10 years. So replaced it with a new KUUMA 6 gal and bingo, same result. Sure hurts to fix something that isn't broken; well the upside is the antifreeze was changed.

Did anyone ever figure out what was happening? I'm bleeding the air out of the lines by opening all the faucets, then pop the pressure line on the tank to make sure it is full to there. The instructions say there should be an air pocket at the top of the tank if you have no expansion tank to allow for heat caused expansion.

Why would air in the lines cause this. The water comes from the bow fresh water tank past the filter to the water pump (checked, it's factory) and then branches off; one branch goes to the cold side of the manifold below the sink and the other goes directly to the water heater. The hot water comes from the water heater to the hot side of the water manifold and there branches out to the galley sink, head sink, head shower and cockpit shower.

Help someone this is driving me batty.

 

[Skipper]

Alternating source pressure fluctuation.
Disassemble the temperature mixer valve. Might be crud in there from, say, an old water heater, that's not allowing the piston to move freely, or the inlet(s) is restricted.
Also, if you have an accumulator, drain it then reconnect it.

 

[CharlieSea]

Hi Skipper, thanks for your reply. There is/are no temperature mixer valve/s. All faucets are two handle; no single handle mixers. The only on off valves are at the tank and the hot/cold manifold under the sink. This is very basic, tank to filter to pump to branch one to water heater and one to cold water manifold. The hot return from the heater goes to the hot water manifold.
Can anyone tell me if they have the on/off valve at the water tank partially closed to restrict the flow?

 

[Skipper]

Hi Skipper, thanks for your reply. There is/are no temperature mixer valve/s. All faucets are two handle; no single handle mixers. The only on off valves are at the tank and the hot/cold manifold under the sink. This is very basic, tank to filter to pump to branch one to water heater and one to cold water manifold. The hot return from the heater goes to the hot water manifold.
Can anyone tell me if they have the on/off valve at the water tank partially closed to restrict the flow?

I meant a tempering valve (pic).
It would be near or attached to the water heater.
I'll assume there isn't one.

Ok, heat up the water in the heater. Then, with the pump off, open all hot fixtures (only).
Turn pump on, let water flow 10 seconds. Turn pump off.
Close all fixtures.
Turn pump on and pressurize the system. Open only the galley sink hot side. See if hot is steady.

If that works, I'll explain why.
If it doesn't, the only 2 things left would be (1) a cracked or corroded manifold, IF the same manifold is attached to both hot cold.
Or (2) you're sucking air at a connection between the tank and pump, without it leaking water.
Edit: whoops, air would cause your issue only if there's a tempering valve.

BTW don't restrict the flow from the tank. It won't help and will only burden the pump.

 

[CharlieSea]

Skipper,
Didn't work. The water system is tight, no leaks and no apparent broken manifold. Tomorrow, I'll check with the manifold maker to see if there its any way the cold could mix with the hot. See file.

 

[chuckwayne]

Tempering valves were not installed by Hunter on the 356, some of us have added them...
the manifold is a pretty robust piece, it's hard to see how there would be crossover without visible external signs.
BTW, it's good that you changed the seaward to a new Kuuma - the seawards tend to leak after about 10 years

 

[CharlieSea]

Hello Chuck,

Thanks for your input. Except for being full of sediment and a little corrosion, the SeaWard was in so so shape. Might have lasted a few more years.

Don't know if a tempering valve would solve the problem. It seems it mixes the hot water with the cold to keep a constant temperature. The problem is getting the hot water to the faucet. With just the hot water on, it starts out hot then as soon as the pump kicks in it fluctuates warm/cool/cold then hot more or less again the pump stops. It's like the cold water supply to the heater is overwhelming the water that should be up at the top of the heater tank. The SeaWard was doing the same thing, so it must be outside the water heater. Or the pump is too strong or the water heater too small. Only thing is then all 356's should have a similar situation. So maybe if there was a transfer in the manifold, that could also do it but it does look robust.

 

[chuckwayne]

I wouldn't expect a tempering valve to fix this; the tempering valve works to moderate the "hot" supply - mainly when using the engine to heat the water because that can be too hot to be safe. However, what you're seeing could be caused by a sticky tempering valve providing too much cold .
since the manifold is bolted together, I would think a leak inside from a crack/bad gasket would always leak, and you wouldn't get the variation .

 

[Stu Jackson]

There is/are no temperature mixer valve/s.

However, what you're seeing could be caused by a sticky tempering valve providing too much cold .

Chuck,

He said he doesn't have one.

Charlie,

I'm thinking about it. New to me, but it sounds like your forensic (detective) work so far is going well, you seem to have isolated the issue away from the heater itself.

The strength of the pump shoudn't be a cause, and if IIRC you have the same pump, where it earlier worked OK, with a new new heater.

Have you checked the troubleshooting guide for the pump?

Do you have a check valve on the cold water line to the heater? [See Calder and the WM Advisors]

 

[Skipper]

Odd, indeed.

Thinking out loud:
There's no temp mixer.
I'll assume all fixtures have the same fluctuation.
New heater.
The manifold is suspect, especially in freezing temps but you're in Miami.
Over-pressure from pump (I.E.: faulty pressure switch) should not cause the symptoms. And being intimate with the boat you would have noticed increased output pressure.
A faulty pressure switch, with a different type of failure i.e. wide pressure range, has been ruled out.
There's no unexpected pump cycling, no air spurting from fixtures, no visible leaks.
There's no other crossover point.
The system worked properly previously, and you've made no changes to it except a new heater which resulted in same symptoms.

If the manifold checks out, please send us a picture of the water heater installation from the plumbing side.