Fitting a Willis Immersion heater

tnegun · 31-05-2022 10:45am

It's currently working away I just want to swap out the valve to remove the restriction but need to find the time to do it! If I was happy to allow 80c water in the tank I don't think I'd have an issue with the lower flow rate I just don't want to risk scalding anyone. If replacing the valve doesn't work I'll look at a thermostatic valve for the feed coming off the tank to control the temperature there. For what its worth the tank will now take 7-8kwh of excess with the willis where as before it was 4kwh max.

You can see the impact of both the diverter and willis here. This is the performance from Saturday the tank was emptied at least once if not twice. Blue is energy usage, where the blue follows the yellow solar production is the diverter soaking up the excess and where the dark blue and yellow spike alternate is the willis cycling in and out to keep the temp below 70c. The back took almost 11kwh of excess solar by the time the day was done.

tnegun · 05-06-2022 8:08pm

Replacement valve fitted, boosting for 30 minutes on a cold tank and the max temp reached coming off the top of the willis was 65c with no cycling on and off. Now I just need some sun!! I also found the fitting guide for my in-tank immersion on the floor of the hot press it can take either an 11" or 18" thermostat so I'll pick one up and swap that in too pity I hadn't found that sooner!

John.G · 05-06-2022 11:29pm

I have (only) replaced 3 or 4 dual immersions for relations/neighbours and none had the thermostat pocket longer than the short (sink) element, ie a 24"/11" ins dual immersion would have a 11" thermostat and a 11" pocket so stick a bit of wire down the existing one to confirm that it will take a 18" stat before purchasing one. Even if you can fit a 18" it will bring its own problems, none, if you are heating a whole cold cylinder (same with 11" stat) but if the whole cylinder is at 65C then if say 1/2 contents are only used, the stat will cut in and you might get very hot hot water in the top 50L or so as the stat is measuring the average temperature over the full 18" length, the same applies to the 11" but not to the same degree, of course the main problem with the 11" is that it doesn't cut in until most of the cylinder vol is used. Interesting to see how it performs if it fits.

John.G · 06-06-2022 9:23pm

Any nice trends this evening?

tnegun · 06-06-2022 10:00pm

I was out all day so just home to check, yesterday was so poor I had to heat water with gas this am. There was one shower from this and one shower around lunch anyway to the juicy stuff. The tank took 7.4kwh and looks clean enough but it did start cycling again around 16:30. The temp probes suggest the feed from the willis was hitting 70c so the pipe stat was opening the bottom of the cylinder was up to 25c at this stage from about 20c so this makes sense I guess warmer water in means warmer water out.

John.G · 14-06-2022 8:20am

How is your system performing now and was it possible to install the longer stat in the cylinder immersion?.

tnegun · 14-06-2022 9:30am

Good averaging 7-8kwh into the tank daily now so plenty of hot water, some days more than is needed others it just meets demand nicely. It still cycles on and off when the bottom of the tank is above about 23c and the level of excess is greater than 2kw but I can live with that. I measured and I think it was 13-14" max for the stat length so I didn't go any further with it.

yannakis · 18-10-2022 4:45pm

Lads this is a lovely thread, good afternoon read!

I've got an Eddi too, and looking into installing a Willis as well so the information shared here is priceless.

Big question though.. Is the Willis suitable for pressurised systems?

https://i.imgur.com/Zb9bzVZ.jpg

The Continental Op · 18-10-2022 5:09pm

Is the Willis suitable for pressurised systems?

No less than any other plumbing fitting. Don't forget that any open system could still have a large static head of water so the Willis would as a minimum need to withstand the same pressure as a grade 1 copper hot water cylinder (80 ft head) which is over 3 bar ~ 50psi.

There is nothing I know of in a pressurised system that is likely to damage a Willis heater particularly as a pressurised system is unlikely to be working at anything over 2 bar.

yannakis · 18-10-2022 10:44pm

Thanks for the quick response. This is what got me thinking, I found the photo that got me thinking. What do they mean by vented systems only?

The Continental Op · 18-10-2022 11:17pm

That could be for several reasons. Might be to do with the potential for over heating and allowing a build up of pressure to be released and also because its often installed at the top of the tank into the expansion feed pipe. If you can deal with a pressure build up because there is no water flowing over the element and the thermostat fails then I think you have covered any potential issues.

The Continental Op · 19-10-2022 3:47pm

If you check the uk buildhub forum you will see the Willis heater sometimes gets used for Underfloor Heating (UHF), one such example https://forum.buildhub.org.uk/topic/18239-willis-heater-for-ufh/#comment-295658 and I doubt many or any UHF uses a vented system.

John.G · 20-10-2022 7:37am

Its being used as a in line (pumped) heater in the above application, its role in heating a unvented cylinder is different, unvented cylinders have a TPRV (temperature and pressure relief valve) mounted on the cylinder and also have a expansion relief valve on the cold feed to the cylinder. The question is, can the Willis Heater be considered part of the unvented cylinder as long as no isol valves on the heater's flow&return piping?.

EVill · 23-10-2022 4:37pm

Slight off topic question regarding positioning of willis. Is there a specific height it should be at? Plumber placed ours just above the hwc. It is not wired yet so can't check it in practice. Thanks

The Continental Op · 23-10-2022 5:37pm

https://www.boards.ie/discussion/comment/119783419#Comment_119783419

imo - As low as possible but bottom of Willis 100mm above the bottom the HWC.

Somewhere I have seen the standard installation diagram

with the min 100 mm shown between the bottom of the Willis and the HWC.

Too high and I don't see it working at all?

yannakis · 29-10-2022 7:38am

So I spoke with 2 plumbers this week, and neither of them is willing to install the Willis on my pressurised system. My next question was the cost of a destratification pump, and the cost for that was ridiculous at €200+ 🙄

Would anyone have a contact that could help me with this upgrade? I'm based in Ashbourne.

The Continental Op · 31-10-2022 10:52am

https://www.boards.ie/discussion/comment/119807148#Comment_119807148

I can't imagine the cost of fitting a Willis heater would be any different? Although the wiring of a destratification pump might be interesting - when does it go on and off and what switches it?

yannakis · 31-10-2022 12:36pm

https://www.boards.ie/discussion/comment/119814713#Comment_119814713

You'd estimate around the €200 to install a Willis? Is that including the device? I was expecting a lot less :| That said, would you know someone who could install it around my area?

The destratification can go on the Eddi as Tank2. When Tank1 (immersion) reaches max, Eddi will start Tank2 until Tank1 starts drawing power again.

The Continental Op · 31-10-2022 1:39pm

The Willis Heater is going to cost around €70 a pump would be a similar cost. For both installs you need to connect to the bottom of the tank so the whole tank may need to be drained down and refilled. The ball valve on the inlet diagram for the Willis is so you only need to drain part way down if you change anything later. The pump will normally have isolation valves on the inlet and outlet fittings. Both need a connection to the bottom and top of the tank. Both need an electrical connection. Therefore I'd assume very similar installation costs.

The Eddi obviously simplifies the electrical connection on the pump.

tnegun · 31-10-2022 2:31pm

https://www.boards.ie/discussion/comment/119815030#Comment_119815030

You will destroy the pump and possibly the Eddi if you wire a pump to Tank 2. The eddi varies voltage and current depending on available solar surplus and is only suited to powering resistive loads e.g. heating elements. You can purchase a relay board for your Eddi to run a pump properly but under no circumstances should you connect it to Tank 2.

yannakis · 31-10-2022 10:24pm

https://www.boards.ie/discussion/comment/119815479#Comment_119815479

My bad there, I already got the Relay Board for the temperature sensors so that's where the pump would go.

Are we not allowed to ask about referrals for plumbers in this thread btw?

Wearb · 31-10-2022 10:58pm

"Are we not allowed to ask about referrals for plumbers in this thread btw?"

Yes, but answers by PM only.

yannakis · 01-11-2022 1:41pm

https://www.boards.ie/discussion/comment/119817253#Comment_119817253

Thanks. So if anyone knows someone who could install a Willis on my pressurised system, give me a shout please.

Coln64 · 05-12-2022 3:35pm

Only just picked up on this. Looks very similar to what I was thinking of doing: so, how is it going ?

tnegun · 05-12-2022 4:02pm

All good so far for me, in fact up to last week I was still getting enough surplus on occasion to heat some water!!

Coln64 · 05-12-2022 6:13pm

thats good news. If I understood the thread correctly, your learning points seemed to be having enough vertical rise above the willis and to use large bore pipe & smooth bends to enable the convection currents to form ? Is that a fair summary ? Did you end up using a pipe stat' in addition to the immersion stat' to overcome excessive cycling / dangerously hot water ?

At the moment I have an iBoost solar pv diverter connected to a bottom mounted immersion ( the cylinder does not have a top immersion heater ) so was thinking of putting the willis in as an external top heater to benefit from rapid heating of the top layer of water.

tnegun · 05-12-2022 8:42pm

Yes that's it exactly larger pipework and try to get rid of sharp turns/bends to help promote circulation. Keep the Willis as low as possible too and joining high up on the expansion pipe seems to be the conscientious too. I didn't really have too much say in that as I had to work in the space I had but its pretty low and joins about 500mm above the tank. I have the pipe stat on and it works much better than the stat in the Willis itself as the internal one is too short and the extremely hot water has left the willis before heating the internal stat so it is ineffective.

Coln64 · 05-12-2022 10:38pm

thanks. Did you place the pipe stat on the hot, flow side or the cooler, return side ? I guess the ( last ? ) question is on "reverse" circulation. When you draw hot water from the cylinder, does it flow back through the willis ? Is it a problem ?

tnegun · 06-12-2022 12:26am

It's on the return side from the Willis, so above it as this is the 'hot' side as it draws cold/cooler water from the bottom of the tank. I know from the thermostats I placed on the Willis there is some short-circuiting occurring when drawing off hot water but it's not noticeable. If available you could use a dedicated feed from the bottom of the tank to avoid this.

Coln64 · 06-12-2022 10:28am

The only pipe stats I can see ( including the EPH one mentioned earlier in this thread ) are designed for switching pumps or valves on or off. They are designed for 230v operation and their switch contact rating might be 16A but they arent designed for the continuous current flow as in an immersion heater thermostat.

Unless you are using the pipe stat to switch a relay to feed current to the immersion ?

tnegun · 06-12-2022 10:27pm

This is the one I'm using its for pumps and hot water cylinders also the Eddi's output limit is 16 amps which matches the EPHs.

Coln64 · 07-12-2022 11:27am

I would be nervous using this to switch an immersion heater, the datasheet says its use is for connecting to a pump or a valve, the load from an immersion is very different to the load on a pump or motorised valve. Its a tricky problem to solve and you have obviously got a good solution with your set up so far. The only thing I can think of is some clever amendment to the pipework above the willis to allow an immersion heater thermostat pocket to be created separately from the immersion heater and to use a proper dual immersion thermostat with set point and high limit controls. But that takes you back to the initial problem of immersion thermostats and their wide switching bands & hysteresis. Alternatively use your pipe stat to drive a relay to switch the current flow to the immersion: but if your Eddi is the same as my iBoost they are very clear about not installing additional switches or controls so even that may be more difficult than it seems.

Wearb · 07-12-2022 11:43am

Any electricians care to comment on above.

I've seen pipe stats used to switch immersion heaters, of course that doesn't mean it correct.

My feeling is that if it's rated to switch that current it should be able to carry it, but I'm not an electrician.

John.G · 07-12-2022 1:22pm

The EPH stat can switch a 16A resistive load like up to a 3.68kw immersion or 4A inductive load, no problem in switching modern circulating pumps, some pipestats can switch 16A resistive but "only" 2A inductive.

Mutley123 · 02-02-2023 1:23pm

Hi all

Thanks for the great thread.

I'm think of installing a Willis and was wondering where would be best to install the upper connection. I understand that some way up the vent pipe is good, but was wondering about the impact of two 90-degree bends (one where it exits the tank, and one where the pipe reaches the wall).

I've attached a photo - if anyone could provide advice one whether higher-up trumps two 90-degree bends I would appreciate it!

The Continental Op · 02-02-2023 1:39pm

I'd replace the rt angle joint where the pipe comes out of the cylinder with a T piece then put in another rt angle to connect to your Willis. However if that rt angle is a soldered joint it might be awkward, but if that joint isn't 3/4 inch (think it might be) then you could up the size of that pipe off the top of the cylinder to increase the flow. So largest diameter pipe possible at the top of the cylinder to a T to feed the existing pipe work and Willis. Others might disagree but thats my take on it.

Mutley123 · 02-02-2023 4:32pm

https://www.boards.ie/discussion/comment/120191614#Comment_120191614

Yes, the existing joints are all soldered so that might be a step too far for my rudimentary plumbing skills. Pipes are 25mm (including the feed pipe from the tank) so I'd planned to use 25mm to 22mm reducing, then a 22mm to 15mm reducer to connect up the Willis heater.

The Continental Op · 02-02-2023 7:00pm

If you replace that hole section by cutting the pipe to the right of the rt angle bend thats a soldered joint you will only need a couple of short pieces of pipe and a straight connector to get the start of the set up for the Willis. Given the small amount of pressure exerted by the heat to move the hot water around the system I'd try and reduce the number of bends ruling out your connection to your highest arrow.

If you go for the lower arrow you are still going to need to remove the pipe coming off the tank to put in your T connection there so you are half way to my suggesting anyway.

TwmSionCati · 08-02-2023 10:26pm

This is indeed a fabulous thread, but there’s something I haven’t grasped, brought up by Mutley123’s “wondering where would be best to install the upper connection”, given his understanding that “some way up the vent pipe is good” [#186]. Why should that even be necessary?

I have a perfectly conventional DHW cylinder with a boiler-fed coil at the base and a 27” electric immersion-heater vertically mounted on the domed top. The element’s now died (short to earth), and can’t be dismounted because too close to the ceiling.

I could of course install a 14” replacement, mounted horizontally in the side of the cylinder, just above the coil, using an appropriate Essex flange.

Or I could install a Willis and direct its output into the cylinder, at roughly the same height, again using an appropriate Essex flange.

The upper connection would be far below the vent pipe: but what's wrong with that?

Regards to all, TSC

The Continental Op · 09-02-2023 2:10pm

https://www.boards.ie/discussion/comment/120217623#Comment_120217623

Willis heater doesn't work that way. Because the force created by the thermo syphon the Willis creates is quite small you need to get a reasonable difference in height between the top and the bottom.

The Willis doesn't heat the water in the same way as the internal immersion. With the Willis the water stratifies in the tank so in effect it heats the water at the top of the tank first and as the thermo syphon moves the water the tank continues to heat from the top down.

iwb · 11-06-2023 9:23am

I learned a lot from reading this thread but went a different way about solving the same problem. Not everyone has a coil in their tank they can use but I did, so I tried this. I started a new thread rather than mess this one up. Any feedback greatly appreciated.

06-07-2023 2:14pm

Hi Guys, in the same boat with solar here and copper cylinder/bath immersion not heating the whole thing. Is adding a willis my best option to get the tank (200litre) full? Although from looking at diagrams I see that it looks to heat water from the top, the same as my current immersion, so how does it end up heating the whole tank as opposed to the current immersion?

Is there another option that would circulate water around the tank that might be more beneficial or is willis the only way to go with keeping the current tank?

The Continental Op · 06-07-2023 2:25pm

https://www.boards.ie/discussion/comment/120813289#Comment_120813289

Because its external and connected to the top and bottom of the tank it sets up a very low powered thermal syphon so it pushes hot water out the top while sucking cold(er) water in from the bottom. Provided the water coming in at the bottom will keep the thermostat below the level its set at it will keep heating the water. It should work no matter what the height of the element in the Wilis is in relation to the tank but the lower it is the better the thermosyphon will work so basically mount it a low as possible.

Ceedee22 · 22-06-2024 10:59am

Hi all, thanks for such a useful thread. I'm still at a bit of a loss on what is ideal in terms of fitting to the expansion pipe. My setup is similar to the previous in having 2 right angle bends but pretty tight in terms of what I can do due to distances to bends. If I fit higher up (30cm or more) on the expansion pipe do ye recon it would cause an issue, versus trying to remove soldered sections and adding a T?

The Continental Op · 22-06-2024 11:35am

My understanding is fitting higher up will be fine and should improve the flow in the Willis. The down side is you are moving heated water through a greater distance of pipework outside the tank that is subject to heat loss so lag it well.

bawnBeag · 16-07-2024 7:54pm

Would this be a good alternative to a Willis? https://www.wrightpumps.co.uk/product/energy-storage-device/

Any thoughts on whether the hot water flow would be impacted?

Jonathan · 16-07-2024 9:48pm

https://www.boards.ie/discussion/comment/122389029#Comment_122389029

Haven't seen that before but it's just a destratification pump so no reason why it shouldn't work. Quite a nice design. And much safer than a Willis heater too.

ctlsleh · 10-08-2024 6:38pm

looking for some advice please……..

I have 2 electric showers at the moment, think one is going to go soon. I have a 40Gallon standard cylinder (about 25 years old), immersion is gone in it, an I have 7kW solar with 5kW battery.

I’m thinking of getting rid of the electric showers when they fail, upgrading the tank and maybe getting a Willis and running it off the solar? I don’t use that much hot water and I can only warm it through the central heating if I want hot water in the house oil boiler) but would like to have it warm at least, esp in winter.

Additionally I was thinking I could have just normal regulated showers and a central pump, although I’m concerned about the noise, as the cylinder is off my bedroom? Upstairs(2 story house, showers are also upstairs so not much gravity)

would I be better to replace the electric showers with individually pumped showers, is a Willis more efficient than an immersion? Would it be worth getting an eddi or just use a timer? What size tank? 2 adults, 2 college kids home at weekends. Approx price to upgrade? Is it worth it?

appreciate any ideas and sugggestions. Thanks in advance….

conor_mc · 10-08-2024 7:15pm

if you have an attic tank then your pressure is dictated by the head (gravity) of that tank, not your hot water tank. We have two pumped showers in a similar setup, works fine.

Re tank size, we bought a house with a down-sized tank for previous owner of about 120l, pain in the backside, stick with a decent family size tank (40 gal = 180 litres or so).

Don’t recommend an Eddy or other complicated electronics with solar feed-in tariff now available, fix up your immersion and get a timer switch to run it on cheap overnight electricity instead.

ctlsleh · 17-08-2024 10:56am

https://www.boards.ie/discussion/comment/122488285#Comment_122488285

thanks, do the pumped showers provide good power, or the same as an electric shower?

Fitting a Willis Immersion heater

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