Q: on Hot water after White Expansion vessel installed

clodola · 11-10-2021 10:49am #1

Hi

I had a 40L white Expansion Vessel installed , old one was leaking bad ; based on the pressure gauge fluctuating I presume the diaphragm was perished since we moved in

Prior to installation of the new Expansion Vessel (White) , hot water would remain hot through out the day (considering temps last week where 18 degrees outside) , alot colder last march , 4-6 degrees ; outside temp is not the factor ; you could not put your hand under the tap after (Heating water for 30 mins in the morning), Thermostat was 60 degrees(has not changed)

**Question**

The plumber just took Expansion Vessel (White) out of the box and did not verify the Expansion Vessel's PSI ; would this be a factor ?

Air trapped in the system?

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Observations

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1) Thermostat , is still 60 degrees for Hot water cylinder

2) The Expansion Vessel (White) , hollow sound off it when tapped , should these fill with some water?

3) Water is a not as hot (before you would burn your hand) now it is luke warm and depletes very quickly (300 liter Bosch water cylinder with inbuilt insulation)

4) Hot water is now scheduled for 1 Hr vs 30 mins before

5) After installation of Expansion Vessel (White), using the Shower in the morning, it did expel air last few days for 10 seconds ; appears to be subsiding

6) Pressure gauge is 25 psi with heating/water OFF

7) Pressure gauge is 20 psi with heating/water ON

8) Pipes coming from the Hot water cylinder are hot , you can rest your hand on them

Cuddlesworth · 11-10-2021 11:30am

Direct hot tap or out of a mixer tap?

If you can, to test, kill the cold water flow at a valve and see if the water comes out hot.

Adding a large expansion vessel to the hot water system could have lead to a pressure differential between the hot + cold systems. If the system isn't balanced, a large difference one could be feeding one into the other instead of just out the tap.

John.G · 11-10-2021 7:26pm

If it was installed properly with the pre charge (air end) pressure at 25psi then if the whole 300 litres was heated to 60/65C, the final pressure would be 31.3 psi, if there was 0 psi pre charge pressure then the final pressure after heating the full cylinder would be 48.6 psi, one way or the other not high enough to lift the PRV on the HW cylinder. If you want to check the pre charge pressure just shut the cold supply to the HW cylinder, and open a hot water tap then check the E.vessel air end pressure with a tyre gauge, also check the location of the E.vessel with respect to the top of the HW cylinder.

Assuming HW cylinder at 30C in the morning then it will require 10.47 kwh to bring it 60C, or a heating coil rating of 21kw, its unlikely that the whole 300 litres would be used down to 30C so assuming 200 litre will require 7 kwh, coil rating of 14kw.

So if you are heating the water with a gas/oil boiler then 30 mins is theoretically OK but I would aim for 1 hour as the cylinder thermostat will stop the heating anyway when the cylinder reaches 60C so no wastage.

Presume you are heating the cylinder with gas/oil fired boiler??.

In relation to "2) The Expansion Vessel (White) , hollow sound off it when tapped , should these fill with some water?"

If the pre charge pressure is 25psi then there will be 5.5 litres in the expansion vessel after heating and 0 litres when cold.

If the pre charge pressure is 0psi then there will be 30.8 litres in the expansion vessel after heating and 25.3 litres when cold.

clodola · 12-10-2021 11:16am

thanks

Yes, heating the cylinder with oil fired boiler

Will set to 1 Hour to heat , comprehend the thermostat will stop the heating anyway when the cylinder reaches 60C so no wastage.

Might check the pre charge , I presume I need to empty the Hot water cylinder tank prior to checking as opposed to just opening the hot water tap

John.G · 12-10-2021 11:44am

Ideally, yes, but if the bottom of the EV is at or above the cylinder top then no problem but if the EV is below the level of the cylinder then just measure (accurately) the distance from the top of the cylinder to the bottom of the EV and I will be able to calculate reasonably accurately the pre charge pressure with the hot water tap (downstairs) open and mains off.

clodola · 12-10-2021 1:30pm

Thanks John

EV is above the cylinder top, just to note , EV was replaced with like for like , same model number / capacity

John.G · 12-10-2021 1:55pm

Very good then, just shut the mains, and open a hot tap below the level of the cylinder and take your reading.

clodola · 12-10-2021 4:57pm

https://www.boards.ie/discussion/comment/118009442#Comment_118009442

this Cylinder is in the Utility room on the ground floor , Hot water tap sits 1/2 height of the Cylinder (thermostat is, tap sits at that level); sufficient ?

1) Close mains

2) Run Hot water tap till empty

3) Use gauge tester to verify it is 25PSI

4) If it is not , pump up to 25 psi or release pressure till it is 25 psi

John.G · 12-10-2021 7:20pm

Yes, I think that should do it.

dathi · 13-10-2021 8:33am

and to comply with part L of the building regulations

1.4.4.4 The hot pipes connected to hot water storage vessels, including the vent pipe and the primary flow and return to the heat exchanger, where fitted, should be insulated, to the standard outlined in paragraph 1.4.4.3 above, for at least one metre from their point of connection.

clodola · 13-10-2021 9:53am

https://www.boards.ie/discussion/comment/118012520#Comment_118012520

Thanks

The Surveyor who looked over the place never mentioned it ; will look into it , no idea if pointless if I cannot access pipes behind walls

I am finding alot of small things like this , rear door no draft proofing , french door not adjusted correctly, big bow in the door creating a gap you can see through ( might as well have a window open), no draft excluder in the cooker extractor pipe, no draft excluder on the external wall vent , it is like having aircon on in the kitchen with a cold wind , front door no insulation around the frame, windows lack of seal between the plinth and frame

It amazes me how these issues even though small and easily fixed , do not impact the BER rating ; its a B2 rated property ; it was freezing when we first moved in, if you have wind passing through; negates the effort and expense of insulation

Next job is to tackle the big draft in the bedroom on a windy day , strange one as the place is full of insulation ; its difficult to verify insulation was present in places after they are covered up , thats the main issue , access to insulate ; this one is worth another thread

dathi · 13-10-2021 1:46pm

it just the first metre from the cylinder out to stop the cylinder loosing heat . also you have two pressure relief valves (red knobs ) and they dont have a tundish which allows you to see when there is a fault and prevents back siphoning into the cylinder.

https://www.youtube.com/watch?v=1nuXmayzIac

Q: on Hot water after White Expansion vessel installed

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