What ho one and all,

I have the boiler and DHW cylinder adjacent to each other in the utility room. Probably less than two metes away, is a toilet with hot water to the basin. The HW pipe, obviously goes from the top of the cylinder, into the ceiling and drops down to the basin HW tap.

Recently, when turning on the tap, based upon the noise from the issuing water, there is considerable air in the system. It does clear but like the Terminator, it will be back. All other HW taps do not have air coming out.

Since it's running at around 3 bar, I assume if air is entering, water is leaking out somewhere? But there is no evidence for that. Where could this air be entering and how can I prevent it.

As an aside, all cold water is mains and there is no air from any taps.

Grateful for any ideas.

Thanks and toodle pip

Is the DHW also mains pressure?
At what temp. are you running the DHW and is it heated by the boiler

If the DHW is at 3 bar it is difficult to imagine air leaking in. If it is mains pressure then I presume it has an expansion tank in the system. These usually have a bladder in them which will in time fail and allow the ballast air into the water. A failed expansion tank bladder would be my first suspect. (assuming there is such a tank in the system).

Thanks to Dr Google, I have checked the expansion tank pressure and it is around 0.75 bar. I believe the incoming mains is around 5 bar, and I do have a PRV fitted to reduce to around 3 bar.

Should I just increased the expansion tank pressure with my car tire pump?

Posted By: RexI assume if air is entering, water is leaking out somewhere?

Not necessarily so. If you remember school chemistry lesson doing a vacuum filtration into a flask the running water tap would suck the air out of the flask but water would not enter. A venturi effect. This could be going on.
The vacuum being the vapour pressure of the water.

Take the car battery out of the car and into the utility room and jury rig a connection to the tyre pump.

Posted By: Rexelectrical pimp

Well worth a try.

My tyre pump came with an adaptor (which broke but I replaced cheaply from ebay), from the cigar lighter to crocodile clips to connect it to the battery. I always use the latter, on the car - significantly better volts/pimp speed, and easier to move around all four tyres without opening doors to re-route the cable.

If you're hooking up direct to a car battery, make sure there's a 10A fuse somewhere in your hookup... !

Why do we put a fuse in a circuit? Yes, to stop things melting and causing fires! Or switches welding themselves so you can't switch them off.

A push-in cigarette lighter plug/socket is inherently designed for low current and short duration use and to get hot and ignite things. There's minimal contact area and no positive 'locking in'.. It's designed on the basis that the car fusebox will protect it from the massive current that a car battery can put out, 100A+

(Compare it with how beefy the prongs on a 13A mains plug are)

Likewise the wiring and contacts of accessories that plug into cig lighter sockets, also assume they have protection from the car fusebox. The cables and switches on tyre pumps are thin and bendy and you wouldn't use them for more than a minimal current in a house wiring.

Just looked on eBay and some of those cheap crocodile connectors come with a 25A fuse and some have no fuse at all. It would be totally illegal to sell flimsy "25A" stuff like that if it were for house wiring, but seems a loophole if it's for cars.

If your plumber had the foresight to fit a service valve you can always isolate the expansion tank, remove it, repressurise it and refit

Thanks for the suggestions. For whatever reasons, the bubbling when the hot water is running has cleared itself.

Regarding re-pressurizing the expansion tank, have yet to do it but the process is in hand.

My wife frequently comments on all the 'stuff' in the garage and that I should have a big clear-out. I have some 3 core cable from various garden items that have bitten the dust. Using one of those 'you should have thrown it away' 5m lengths of cable, I will splice it into the twin core of the car tyre inflator so that I can get the pump next to the expansion tank and run from the car battery.

Will post when the job is complete.

3 bar is only 45psi - high for a car tyre but normal for vans, caravans. So something wrong with your pump. I have an excellent Ring one.

Sounds like a bicycle tyre pump might do the job, and provide free exercise

My 1935 brass and cast iron Dunlop Major foot pump is superb - but the Ring one has some advantages.
.

Posted By: RexCould I have increased the resistance to the point that it does not work so efficiently?

I was wondering something similar. That might be a reason to move the battery to the tank, as suggested earlier.

Please put a fuse in the circuit!! Don't start a fire in your utility room.

Actually, please go past a cycle shop and grab one of the new style rechargeable bike pumps that fit in a bike bottle carrier. They are a great innovation and not expensive at all.


Edit to add: 5m double length of mains cable with connectors has resistance around 0.5ohm (depending on cable size) so yes that would be enough to knock a couple of volts off the supply. Doesn't matter at all in mains wiring, but could well be a problem for car wiring where the voltage is less and the current is more.