Fitting a Willis Immersion heater

tnegun · 11-05-2022 11:04pm

I just boosted for 5 minutes there and the stat didn't cut in to stop it heating. I took the temp of the feed pipe from the bottom of the tank and it was 21c after 5 mins heating the return pipe was 57c. The heater made a low kettle sound throughout and from placing a hand on the feed pipework I could feel the flow. The whole time the bottom of the Willis chamber remained cool to the touch while the top was quite hot.

John.G · 11-05-2022 11:30pm

I don't see anything wrong with that, dT, 57-21, 36C, flowrate, 3X860/60/36 = 1.19LPM, perfect IMO as the return/tank temp should remain at 57C until the the tank bottom reaches 24C which it shouldn't do until cylinder practically full of hot water. If you are happy with this, you might care to keep boosting until stat cuts out and/or then set the stat eventually to 65/70CC and you are in business?. Remember that once HW is drawn off that the tank bottom will then, in summer, be ~ 15C so return will be 51C, in winter, bottom may only be say 7C so return/cylinder will be 43C which you need as a minimum.

Forgot to ask, any short circuiting when drawing off HW?.

tnegun · 12-05-2022 8:51am

Excellent points I think it might just take a little getting used too as we're not used to having such hot water in the house! There doesn't seem to be any noticeable short circuiting occurring either.

John.G · 12-05-2022 9:09am

You might also note the dT when the diverter is only inputting say a kw or so, (if that's how it works).

The Continental Op · 12-05-2022 9:22am

Wouldn't a Thermostatic Mixing Valve on the hot outlet of the HWC reduce the problem of any accident with very hot water?

tnegun · 12-05-2022 2:10pm

Ok so I must have messed up my measurements last night or didn't give it long enough but the return pipe is hitting 85c when run off running solar today. I was looking at the mixing valves previously but I think I'll try replace the 1/2" return with 3/4" first.

tnegun · 12-05-2022 2:11pm

https://www.boards.ie/discussion/comment/119049764#Comment_119049764

The diverter varies the output from 0-3kwh I'm wondering if lower is getting too hot and not generating enough circulation

John.G · 12-05-2022 2:18pm

https://www.boards.ie/discussion/comment/119051258#Comment_119051258

Is the cylinder hitting 85C as well??, if it is, can't understand why the stat isn't switching off the power,

The Continental Op · 12-05-2022 2:22pm

I know it shouldn't affect it but that Willis heater could have been sitting on a shelf for years so perhaps the stat isn't working?

tnegun · 12-05-2022 2:43pm

https://www.boards.ie/discussion/comment/119051335#Comment_119051335

At the top yes but the bottom is still cold.

https://www.boards.ie/discussion/comment/119051371#Comment_119051371

Possibly but the bottom of the Willis is cold to touch so I think the stat isn't getting to temperature to cut it out.

The Continental Op · 12-05-2022 2:50pm

Another possible option is to move the Willis higher in relation to the tank. That way the stratification in the tank should affect the thermostat in the Willis sooner?

John.G · 12-05-2022 2:53pm

Yes, but the stat is a long rod that extends the full length (height) of the element which in turn extends into the willis cylinder to 80%??? or so of its length. I would remove the immersion lead and check for continuity (resistance) while turning the stat up and down.

The immersion head is on the bottom?.

tnegun · 12-05-2022 3:51pm

https://www.boards.ie/discussion/comment/119051636#Comment_119051636

Yes the immersion is on the bottom, some good news the stat is working I just checked and we were exporting power. I checked the temp of the feed pipe by hand and it was warm to touch so at least that confirms its working. However I touched the bottom of the tank and it was cool my temp probe says 25c. I drew off some hot water and there is definitely some short circuiting as the feed on the Willis then became cool and the stat closed and it began heating again. I suspect this happened was the stat closed or there is no surplus to power the Willis so the temp in the Willis stabilized and the flow reversed slightly as hot water had entered the feed piping.

Just on the stat going the full length when its heating the bottom of the Willis is cool to touch but the top very hot would this impact its operation?

Tomorrow I'll only use the Willis today I had the tank immersion on first and only when it reached temp did the Willis start heating today not sure it will make much difference but it will be interesting if its the primary heat source.

The Continental Op · 12-05-2022 4:20pm

Why not use the tank immersion? Did I miss the reason? Would not a double pole mains relay make the switch over automatically if energised by the diverter?

John.G · 12-05-2022 4:24pm

Bit of a mystery getting a temp of 85C. Is it a dual immersion (still) and separate from the diverter, ie is it operating in stand alone mode with either sink or bath selectable and is the Willis just connected to the diverter but can also be boosted for 5 minutes as well?.

What may be affecting the willis circulation is the temperature of the water in the top of the cylinder, ie if main immersion had the cylinder top at say 58C and the willis then is switched in then it's bound to affect the circulation IMO as the already heated water won't move downwards to allow circulation?. As you suggest, just use the willis for now and monitor its performance.

John.G · 12-05-2022 5:14pm

https://www.boards.ie/discussion/comment/119052101#Comment_119052101

see post #1.

tnegun · 12-05-2022 5:24pm

https://www.boards.ie/discussion/comment/119052101#Comment_119052101

The immersion isn't heating the full tank from the diverter it typically only takes about 3.4-4kwh, the idea of the Willis was to heat all the water and its already having some effect as 5.5kwh went into the tank today.

https://www.boards.ie/discussion/comment/119052123#Comment_119052123

The bath element of dual immersion is connected as heater 1 on the diverter and the Willis is heater 2. The diverter has the ability to boost either heater on demand. The diverter is configured to use heater 1 until its satisfied(it detects the stat opened and no current is flowing) and then switches on heater 2. I've changed the priority to heater 2/the willis first for tomorrow.

The Continental Op · 12-05-2022 5:25pm

That was a long time ago 😣. I therefore assume this is a very big tank or it won't take a 36 inch element (sometimes the coils interfere) ?

If the OP is thinking of going to the lengths of destratifing the water in because of the Willis then why not just mix up the water that the existing element was heating?

Only asking what seem obvious questions to me but I'm happy if the OP preservers with the Willis as its very interesting.

Edit> Sorry tnegun you posted just before me.

John.G · 12-05-2022 8:27pm

https://www.boards.ie/discussion/comment/119052393#Comment_119052393

So, if no Solar PV you can also feed either the "bath" element or now, the willis, from the mains elec?, if so, can you just feed the Willis now from the mains and see/monitor it until cut out and a tank full of hot water (hopefully).

Also re dual immersion, there is normally only one stat on this which switches the negative so that it switches either sink or bath element on/off (whichever is selected with the sink/bath c/o switch). So if so and you selected "sink" you could boost this first and then it should change over to the Willis?. I'm just thinking about that 85C, we know the Willis stat is operating but hopefully someone hasn't just wired the diverter straight into the bath element and by passed the (dual immersion) stat.

tnegun · 12-05-2022 10:06pm

Yes with no solar I can choose either heater to heat and yes my dual immersion is the same before I connected the willis the bath element was on heater1 and sink heater2 and worked as expected cutting out at 65c or so. When I connected the willis I disconnected the sink feed at the diverter and connected the willis in its place. I never had any issues with water temperature until I added the willis so it must be poor flow through it. I tried the willis again tonight for 20mins and it got to 85c at the top so last nights 57c had to be a bad reading. I've young kids so before I let the willis heat a full tank to that temp I'll change all the return piping to 3/4" and see what impact that has.

John.G · 12-05-2022 10:18pm

And the Willis stat is set to ~ 60C?.

Circulation is too low in any event at ~ 0.66LPM to give 88C so changing to 3/4" should help.

tnegun · 12-05-2022 10:36pm

Its set to 65c there was a sticker on it saying set at factory so I didn't change it. From the info sheet included with it the immersion is 10", the thermostat is 7" and the safety cutoff is 85c. I ran it again there and the bottom of the willis is 21c, middle 55c and top 84c. If it helps the exact one I have is an Ideal Emerald Geyser. Bought here https://heatingpartsdirect.ie/products/willis-external-immersion-heater-ideal-710536 edit. I linked the wrong heater fixed now

The Continental Op · 12-05-2022 10:49pm

Can you swap the immersion on that one or is it a sealed unit?

tnegun · 12-05-2022 10:52pm

I didn't inspect it closely enough to be sure before fitting are you thinking a smaller element?

The Continental Op · 12-05-2022 11:02pm

I was asking really because I want one that has a standard 2-1/4" immersion so I can take it out to replace it. I know when I was looking around for one there was one model that I read a review where it was suggested the immersion and the copper "can" were a sealed unit. Looking at pictures of the Emerald Geyser I don't see the hex head I'd expect to see on an immersion to screw it in or out.

This was the one I was hoping to get hold of https://www.stevensonplumbing.co.uk/willis-external-immersion-heater.html but I know the local heatmerchants has a few various ones hidden covered in dust on the top of a storage cabinet so I'll see what those are like first.

John.G · 12-05-2022 11:17pm

https://www.boards.ie/discussion/comment/119054530#Comment_119054530

The average of the 3 temps is 53C so the stat may cut out by reducing the setpoint to say 50C but again this is really not satisfactory as if it does cut out and you don't draw off any water, it might take a long time for it to reset except that you are drawing off some HW to short circuit some cold through the Willis. Ideally, the dT through the Willis should be ~ 35C to 40C to allow continuous operation until the return temp is above say 25C to 30C, increasing to 3/4" will certainly help but the horizontal runs are possibly the biggest problem re circulation so try and get them inclined a bit.

The Continental Op · 13-05-2022 12:14am

Odd question OP do you have a Surrey flange on the cylinder? You'd only really see them installed on a copper tank. A doohickey to prevent air getting into the the hot water coming from the tank, helps improve the life of show pumps afaik?. Its something that might affect the flow of water? Didn't think they were common in Ireland but I see screwfix and heatmerchants have them https://www.screwfix.ie/p/salamander-pumps-s-tank-flange-fitting-for-hot-water-cylinder-22mm/76906 & https://www.heatmerchants.ie/1-warix-flange-u80279. I believe some tanks come with a similar fitting as part of the tank?

tnegun · 13-05-2022 9:10am

No surrey flange from what I can tell it looks like a regular take off at the top of the tank, the shower pump is fed from a second 1/2" take off slightly lower the the main one. It's actually this pipework and the location of the pump that cause me the most trouble as I need to work around them hence the 90 degree to a short horizontal at the top of the willis. I'm planning on doing the following!

Lowering the willis in relation to the tank right now the top of the willils is just slightly lower than the top of the tank.

Replace all the return 1/2" with 3/4"

Rise straight out of the willis for approx 500mm and then have the horizontal run at an angle if possible to the expansion pipe

The Continental Op · 13-05-2022 9:36am

It shouldn't make any difference if you connect a bit higher up on the vent pipe if that helps you make a more direct run. Provided the hot water can rise cold water will come in and replace it below so you don't need to connect as close as possible to the top of the tank.

The Continental Op · 13-05-2022 9:56am

Note: Slightly off topic but interesting.

I went digging around for more Willis info didn't expect much as I've done it so many times before but I did come up with an interesting highly technical report on the Willis "Solarsyphon" (not an immersion its a water to water heat exchange which installs in the same way). For anyone interested here. Its all very technical but if you look at the pictures you can see the the flow pipe is connected quite high up to the vent pipe.

Fitting a Willis Immersion heater

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