immersion heater hot water problem

Canucklehead

birkee wrote: »

My last post disappeared into the ether. WAS rather longer.

Cold water feeder tank, and H/W tank both in the loft,, means no water pressure to feed the H/W tank.
You need at least 6 feet height of cold above the H/W tank to create reasonable pressure.

I think you'll find it's the CWSC water level to outlet (tap spout) that is the governing factor in the pressure you will get from a gravity system.
( There will be some frictional loss though the cylinder and additional pipework if you want to get picky )

Since the OP can't get photos then it's all whistling in the dark as to the cause of any air lock.

I'll give it a go though.

Insufficient stored cold water.
The draw from a bath tap is greater than the cold feed can provide so air is draw down the open vent. = Upsize the cold feed to 28mm.

When you run a bath does the hot side 'spit'/splutter?


GSR.

keystone

Canucklehead wrote: »

When you run a bath does the hot side 'spit'/splutter?

Kitchen does - post #1.

Cheers

DVardysShadow

Canucklehead wrote: »

I'll give it a go though.

Insufficient stored cold water.
The draw from a bath tap is greater than the cold feed can provide so air is draw down the open vent. = Upsize the cold feed to 28mm.

I agree with this - except that there probably is sufficient stored cold water - just not the pressure to get it into the storage tank. The cold water feeds into the bottom of a hot water cylinder, but is drawn from the top, so it is very likely that there is not enough head to keep the cylinder full to the top when hot water is drawn - instead, exactly as you say, the vent pipe drains down.

OP: what is the vertical height between the water level on you cold water storage tank and the vent pipe/drawoff connection from you hot water cylinder?

keystone

I'm also interested in the proportion of horizontal pipework to vertical pipework. Eventually they get good flow at the kitchen tap.

Cheers

Canucklehead

keystone wrote: »

Kitchen does - post #1.

Cheers

Only initially to clear the air.
I'm interested in what happens when it's been running for a while.

Once air is clear from a pipe it stays that way.

Air is being drawn in somewhere.

GSR.

keystone

Canucklehead wrote: »

Only initially to clear the air.
I'm interested in what happens when it's been running for a while.

Once air is clear from a pipe it stays that way.GSR.

Yes take your point. I'd interpreted post #1 as saying once its clear all taps run fine without further problem.

Air is being drawn in somewhere.

Indeed so.

Cheers

birkee

keystone wrote: »

Mmm - how does a Fortic tank work then?


and when you pump out the HW cylinder faster than the CWST can replace the water taken out?

Cheers

New installation. Thought fortic tanks were finished, due to their inefficiency? OP need to state tank type.

You don't pump out the cylinder. It's not a vacuum pump 'sucking' water out. The pump is in the outlet pipe, and can only pump what the cold water pressure header tank drives out of the H/W tank to the pump.

keystone

birkee wrote: »

New installation.

Not the point.

Thought fortic tanks were finished, due to their inefficiency?

Nope but equally not the point

OP need to state tank type.

Not relevant to my question. You said that it was necessary fior a minimum 6 foot 'twixt cold tank and hot cylinder. So I asked how does a Fortic tank work then?

You don't pump out the cylinder. It's not a vacuum pump 'sucking' water out.......

Yes I know. Do you not understand why a minimum 50 gallon CWST is required when you have a pumped shower then?

Cheers

DVardysShadow

birkee wrote: »

... You don't pump out the cylinder. It's not a vacuum pump 'sucking' water out. The pump is in the outlet pipe, and can only pump what the cold water pressure header tank drives out of the H/W tank to the pump.

There is no major distinction between a 'vacuum' and a 'pressure' pump for liquids. The pump will put a pressure difference across itself - if the outlet side is an open tap downstairs by several meters, the pressure at the outlet of the pump will tend to be at a lowish pressure and the inlet side will be at an even lower pressure. The pressure across the pump for a particular flow rate will be the only given in this problem

The net effect will be that if the cold water tank does not have the head to create an adequate flow into the HW cylinder, then the pump will draw from the vent.

sat56

Wow thanks for the replies.

I will try get photos tomorrow evening or at least a diagram.

In the meantime ive done as post 5 suggested and forced mains water up the hot water system from the washer connections in the kitchen. gave it 3 x 30 second bursts. no overflow spillage was seen. I will see if that makes a difference in the morning.

The height of the top of the heater is only inches below the base of the hot water tank.