Altered header pressure resulted in reduced capacity

[Boobah]

Hi
Im new
I may amuse any experts with what follows

i sawed in half a vented direct immersion boiler (which supplies hot water in property with eco7) and elevated the feeder tank into the loft. Both the tanks are intact (no new openings). I reconnected the severed pipework, the only difference is the header tank sits 25cm higher than it used to relative to the heater tank. Both tanks are 70cm higher relative to the taps. I didnt opt to move entire system to minimise heat loss in cold attic.

There is better pressure to shower now but far less hot water capacity. I gauged this with a full bath, a volume of which im familiar.
What happened? My only theory is that the feeder tank has a stainless steel braided flex hose for the water feed in and that’s perhaps creating bottleneck. Maybe the new higher hot water pressure empties tank faster than it fills? and somehow this traps air inside - I don’t know the mechanics of inside the boiler.

Anyone whos lived with vented system knows that at the end of the boiling cycle there is a momentary bubbling, whilei dont know the physics involved, when this happens now, the tank sounds emptier/more hollow judging by the reverb inside the tank.

Any ideas?

 

[pcaouolte]

Any photos of this new setup which might add to our amusement?

 

[Madrab]

i sawed in half a vented direct immersion boiler

Are you seriously saying you took a hot water cylinder and cut it in half?

So from this >>>>>>> To Like something like this?
>>>>>>

 

[Boobah]

the tanks were not compromised. The unit was factory constructed with a header tank soldered to the bottom portion (shown) with copper standoffs. I just cut the standoffs and the vent pipe and cold feed pipe. The cold/header feed pipe (from header tank directly above) is seen in the attachment. The vent pipe is behind also leading to header tank above.

 

[Boobah]

Im happy that i have a shower now after years of only a bath. The shower runs hot for 30mins before it runs cold.

Its just that when i run a bath it looks like there is 50% less water before it runs cold.

Header tank is 2m above the ‘basic’ 1:1 shower/bath mixer tap

Is there a correct procedure for emptying /refill these systems? I have cold feed stopcock and drain stop cock in the cupboard. Can air get trapped?

 

[trojanhawrs]

Is your vent pipe hanging over your cold water tank well above the level?

 

[Boobah]

No, the pipe extends not any higher than as it was manufactured (in the pic attached, the pipe thats lagged is the vent, to illustrate )

 

[trojanhawrs]

What size is that tank anyway?

 

[Boobah]

110L + 20L

 

[trojanhawrs]

Well that's probably about half a bath so wouldn't be any great surprise if you can't fill it. It's possible you're emptying faster than the cold replaces it but it should just suck air through the vent pipe. It's possible with you moving the cwt higher the vent pipe is now too low and it's trying to suck water and created an air lock. Take the lid off the tank and either raise the vent or lower the float and see if that makes a difference. Try to ensure the new vent pipework between the tanks is constantly rising.

 

[Boobah]

Thankyou for the input.

Im familiar with how much hot water it produced before the modifications because i had baths regularly.

I might replace the mains pressurised braided hose (which feeds header) with 15mm pipework to see if that changes anything. The design of it is shown attachment (see small opening). I’ll fill bath with tap half open to see if i get more hot water ….

Theres no bends in the vent pipework its straight up vertical.

 

[Boobah]

You make a good point about small capacity. However the heated tank should have 110L (quick search suggests bath is 150L) ….
Each time i tested, no hot water was used prior on that day

I’d honestly say that the bath looks 50% full of what the system produced before.

Maybe in the previous setup the residual heat in the internal metal warmed up enough ‘extra’ water while flowing at slower rate.

More tests to follow (run bath tap half open)

 

[Boobah]

. It's possible with you moving the cwt higher the vent pipe is now too low and it's trying to suck water and created an air lock.

Hmm. The vent pipe extends higher than before but it open end is no higher than the header (its conjoined to it).

Take the lid off the tank and either raise the vent or lower the float and see if that makes a difference.

The lid is off the entire time (actually the 40mm pvc header overflow isnt currently connected - yet to do it).

What is lower the float? You mean depress it to add extra water?

 

[ericmark]

I have found my immersion heater only heats top of tank, where the boiler seems to heat all of the tank, I have looked at the combined cylinder and header tank, wonder what insulation is between cylinder and header tank, is the header tank water pre-heated?

I look at the picture

and wonder if worth getting a tank with two immersion heaters, or is the Willis system

with an exterior immersion heater a better option? Rarely have a bath so don't really need a lot of hot water, immersion only used in summer, to use excess solar, so not enough hot water on a good day, to bridge the gap on poor days, the immersion heater controller is designed for two immersion heaters, (iboost+) but the Willis is likely to heat more of the tank.

 

[ericmark]

I do have off-peak, but not economy 7, I only get off-peak for 5 hours. But I don't use off-peak to heat my DHW supply, in winter can't stop boiler heating the DHW so loads of hot water, boiler is C Plan, summer however more of a problem, as to how to improve still under consideration.