hot water pressure

[grahama]

just fitted a calorifier and can’t get a good steady pressure from the hot water taps:-

• water drops off to a trickle before the PAR Pump, fitted cold water side of the tank, kicks in to build up the pressure again, then it’s fine for about 5 seconds before the pump stops, drops to a trickle and the cycle is repeated.
• temporary fitted an accumulator from a friends boat to the cold water feed to the calorifier, makes the problems worse – just takes longer for the pump to kick in but effect is exactly the same – just the frequency is reduced, removed and returned to friends boat
• calorifer has a blending valve, to regulate the max temperature of hot water and when this valve is set so the temperature is the hottest the effect is at its worst, turn the valve so temp is minimum then pressure and flow at the hot taps is more constant and even
• the pump has no trouble keeping an even nearly constant flow from to the cold water taps and if I keep the pump running (linking out the switch) the hot water flow is also constant and even.

my theory is that the calorifier is acting as a large buffer volume (24litres) and as such when a hot water tap is opened the resulting drop in pressure takes a long time to be seen by the pressure switch mounted in the pump body.

How are other peoples systems configured?

Is it normal to have a pressure switch in the hot water distribution pipe work to feed forward the start signal for the pump.

Any help would be very welcome

 

[snowleopard]

Have you added a non-return valve to stop the hot water running back into the cold system? If that's in the wrong place relative to the pressure accumulator it gives problems. Also some non-return valves need a lot of pressure to open and that could be turning off the pressure switch on the pump.

 

[aluijten]

Could it be there is some air caught in the calorifier? This would act as a accumulator on itself.

Arno

 

[nedmin]

Keep it simple,why limit your hot water temp.it will give you more hot water by diluting with cold to get the right temp.you shouldnt need a non return valve.all visitors are warned that the hot water can get very hot if they dont dilute it.Its not as if the general public come on board.

 

[grahama]

there is an old original non return valve fitted prior to the calorifier, I did dismantle it and I can't say I thought it was very effective.
The system has been bled correctly, there is no trapped air.

 

[Nich39Nige]

Strange one Graham, I have the same problem on Shearwater. I'm in Baku until 14th Aug and I'm getting the guy who installed the new calorifier to check it out as I've tried everything!

Just another hiccup.

I'm still planning to slip and proceed to waters new in September.

Nige

 

[grahama]

Hi again Nige,
I fitted the calorifier myself, new teak pads onto hull etc, took ages but I even managed to get the cal level as stated in the installation manual, I've done a neat job just this last hiccup. It's an Isotemp Basic 24 litre one.
Some very experienced friends are also puzzled.
Has yours still got the one way valve fitted near the exhaust riser
Graham

 

[Nich39Nige]

Graham,

Yes it has but that isn't the problem. I've dismantled the whole system, put new olives in, bled and rebled the calorifier, replaced the pump, fitted an accumulator and still have the problem.
Time to call in someone who may know something I don't.

Nige

 

[grahama]

Nige,
If I, or you, solve the problem I think it would be a good idea to drop a PM, am going go look at other friends installations next weekend to see if anything jumps to mind, good kuck
Graham

 

[jjc]

The temp limiting valve should be in the primary circuit (the one to the engine) and so should have no effect on the secondary circuit (the one you get the hot water from) so if this is changing how your taps work then I think you have it connected wrong.

John

 

[Ships_Cat]

The pumps normally cycle like that if there is a severe restriction between the pump and the taps. Assuming no blockages, and it seems that is so, I would suspect the temp regulating valve - not saying it is faulty but perhaps its mode of operation or incorrect installation.

I sympathise with the comment by another and would be inclined to throw it away in any case. We don't use one and don't find it a danger.

John

 

[grahama]

jjc,

no the temp limiting valve is not incorrectly installed, supplied like this from the manufacturer and is a mixer valve to limit the max temp to hot water taps - thus conserving the hot water from the tank, it is a link via a mixer valve from the cold fresh water into the tank and the hot fresh water out of the tank.

 

[HeadMistress]

Grahame, is there any chance you plumbed in the calorifier backwards? You would't be the first person to do so, 'cuz it's counter-intuitive--the opposite of the way most tanks fill and empty. The cold water inlet from the water tank/pump SHOULD be connected to the fitting at the bottom of the tank, hot water outlet at the top. If you reversed it, that would account for your problem.

If that's not the problem, you may have just tried to run hot water too soon. It's important to turn the water pump on and leave it on without running any water till the water heater tank has completely filled...and it needs to stay full--continually replenished by the water pump. Leaving the water pump off all the time except when you want to run water can also account for your problem, 'cuz when the pressure TO the water heater drops, water from the outlet at the top of the water heater will drop too.

It's also important to turn on all taps and let water run (you don't have to heat it) till all the air that got into the plumbing when you installed the water heater is bled out of the system. Air pockets in the plumbing would account for your problem too.

If none of the above, contact the mfr.

 

[Salty John]

The symptoms seem to indicate that the pump is falsely seeing adequate pressure on the hot water run, so there is some kind of restriction in the run - tape from a joint, debris in the piping or in the pump etc. I would suspect an airlock, but the pump runs when you by-pass the switch so a physical blockage seems more likely. The pump is capable of overcoming the restriction, but at a pressure that is at the top end of the pressure switch setting.

 

[cliff]

[ QUOTE ]
jjc,no the temp limiting valve is not incorrectly installed, <font color="red">supplied like this from the manufacturer </font> and is a mixer valve to limit the max temp to hot water taps - thus conserving the hot water from the tank, it is a link via a mixer valve from the cold fresh water into the tank and the hot fresh water out of the tank.

[/ QUOTE ]Just because it came that way does not mean it is correct. I suggest you reverse the hot and cold feeds to the valve - you should have two inlets and one outlet. sounds like the feeds are possibly the wrong way round.

I also recommend fitting an accumulator of at least 8 litre capacity - these wee 1litre jobbies are NFG.
----------

“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo

 

[Ships_Cat]

Not saying the temp limiting valve is incorrectly installed or even saying it is not operating correctly, but just that if you are sure there are no blockages or airlocks elsewhere (as you have said is the case), that valve would be my first port of call as it will impose a restriction.

Just because they may work on some other boats does not mean that they will work on yours (for example, your pump may be of lower pressure, more pressure loss in your pipework, etc). To eliminate it from the equation my first reaction would be to take it out - can always put it back if it is not the problem and wanted.

John