Airlock in hot water system (Willis heaters)

Murph_D

I have a couple of willis heaters that provide my hot water. For those not familiar, these are small kettle like units that heat the water and feed it into the hot water tank, as opposed to an immersion heater that heats the water inside the tank. My plumber persuaded me at the time that they are better, can't really remember why!

Lately I've been hearing a knocking sound in the pipes after they heat the water and there is far less hot water produced than before - I'm thinking the sound is some sort of airlock between the heater and the tank, or in the tank itself.

Is there a fairly straightforward way to fix this or do I need to call the plumber in?

TIA

Wearb

https://www.boards.ie/discussion/2058243718/fitting-a-willis-immersion-heater

Maybe you will find something on this large thread.

John.G

https://www.boards.ie/discussion/2058261697/airlock-in-hot-water-system-willis-heaters

Its possibly a build up of limescale especially if installed some time ago. Any photos of your set up?.

Murph_D

https://www.boards.ie/discussion/comment/119564065#Comment_119564065

Thanks for that, interesting thread alright. I should have mentioned my system is in place 15 years and had been working fine until recently (although scalding water was always a problem, that seems to have gone away...)

John.G

What diameter piping are you using?, in the other post success wasn't met with until pipework increased to 3/4" and a pipe stat installed.

Murph_D

The willis heaters (there are two in parralel) have ½" inputs and outputs, all of which are connected into ¾" pipes feeding and returning from the hot water tank.

Sorry about the orientation. Limescale was a problem before - these heaters were swapped out once already but we have a water softener system now.

What happens is they heat up but water not getting to tank - I know this as the Willis feed pipes at bottom get hot right away and thermostat kicks off, so the hot water is not circulating from the heat. Can hear water boiling in pipes. Am thinking my have to drain tank? There’s a valve there beside the heaters.

John.G

You don't need to drain the HW cylinder as long as the 2 heaters isol inlet gate valves are holding tight, just shut them and the cold water into the HW cylinder and open a HW tap downstairs, you can then remove the heater for strip down inspection but if you want to inspect/clear right back to the HW cylinder cold water inlet/outlet to the heaters then you have to drain down the HW cylinder,

That horizontal pipework coming off the heater(s) top(s) definitely IMO slows down circulation, you should be able to install a few 45 deg bends to angle that upwards or a pipe benders might do a even better job.

Also, if no improvement after carrying out the above you might consider (temporarily even) running both heaters (electrically) in series, ie take the neutral from one heater and link it to the positive in the other heater after removing that heater's supply, you will now effectively have two 1.5kw heaters that might circulate without the stats cutting out until the whole cylinder is up temperature?. 3kw continuous power might heat up the cylinder far quicker than 2X3kw elements switching in/out very often.

Murph_D

https://www.boards.ie/discussion/comment/119565684#Comment_119565684

https://www.boards.ie/discussion/comment/119571451#Comment_119571451

Thanks for this, but maybe I'm not being clear - this was all working fine until recently, and there is nothing wrong with the heaters, they are correctly heating the water and cutting out when the return is hot (which is happening quickly because the water is not circulating out of the heaters so it actually heats back along the cold input before cutting out).

Anyway I won't be tackling this myself - I'll get the professional in. I've never been delighted with the Willis anyway to be honest - I'll probably just have a dual immersion installed instead.

John.G

Ideally, they should give a temperature rise of ~ say 40C, if you start off with the cylinder at say 20C then the temperature of the water is 60C going into the top of the tank and you will get hot water available almost immediately, eventually, the whole cylinder will heat up, from the top down, the heater stat set to say 70C will then cut off the power once it sees the heater inlet temperature reaching ~ 30C.I have always reckoned that 3kw is too powerful to keep the dT to 40C and 2kw would give far less hassle.

If you have a blanked/plugged immersion port in the cylinder top then a dual immersion would also be my choice, you will get ~ hot water relatively quickly with the sink element, ~ 30 litres @ 40C in 20 minutes or so.

Bass Reeves

If scalding water is an issue at the taps you should get installed a mixer thermostat at the hot water outlet from the hot cylinder. This mixes hot and cold water and you can regulate your hot water to an acceptable heat at the taps.

We have solar hot water tubes. This was installed when they were installed. They save an amount of hot water