Solar water heating system playing up

[The Natural Philosopher]

leave it to rot.

It will protect the tiles underneath a bit.

[cynic]

If the pump is not running the sealed system primary water in the panel will heat up and vapourise thus the pressure will rise far higher than the norm. My system is somewhat younger than yours and has a controller which compares the temperature of the top of the panel with the temperature in the lower part of the cylinder. When the panel is more than 5 degrees above the cylinder the pump runs. If the cylinder is already hot right down to the bottom the pump is inhibited and vapourisation takes place, however the expansion due to vapourisation is conveyed into a seraled system expansion vessel. The expansion vessel is capable of taking all the expansion which might occur. I agree with others that the pump not running is the most likely cause of your trouble but this may be due to a control failure rather than a pump failure. Myson is not one of my personal favourite pump manufacturers but others may disagree

[les]

Thanks for that. Just been investigating, it may be more than the pump. It's 8am and the digital temp gauge in the airing cupboard is showing

55c at the sensor on the panels, 15c in the tank. I have checked the hour counter (its got a counter which shows how many hours its run since install - not sure why) - no change in hour setting since yesterday. If I turn off the power supply to the system and leave it a minute or so and turn it on then the green light comes on and starts the pump. After about 40 seconds it switches back to red light and the pump goes off. Not sure what that could be - the temp sensors appear to be working. Not sure how the system works and am wondering if the pump was failing and stopped then would this have some sort of feedback and close the system down, or is it more likely a switching fault? My gut reaction would be a switching fault. Will feedback later when I have clambered about in the loft a bit more.

[David Hansen]

On Sun, 31 May 2009 00:18:27 -0700 (PDT) someone who may be les wrote this:-

Can you identify the make and model of controller?

As others have said the controller compares the temperature at the panel and at the cylinder and turns the pump on or off. I would look at the controller and find out how to turn the pump on manually, all controllers should have this for installing and testing the system. Then you can test the pump.

It is extremely unlikely that there is any feedback from the pump.

It is also a possibility that the controller settings have been altered somehow.

[Dave Liquorice]

Directly I agree but there could be a current monitor that shuts the system down with a stalled pump or even some "smarts" that expects to see the temperatures at the panel sensors change by X degrees, Y seconds/minutes after the pump has been switched on.

Running for 40 secs then shutting down indicates some form of fault detection cutting in. Note "fault detection" could be a 2 year "I need maintance" timer kicking in, like those that have been known to be fitted to alarm systems...

[les]

I can feedback a bit more now, have isolated the pump to mains only and switched it, it runs ok. - so pump seems ok. The System controller is a Resol EID temperature differential controller and it is located in my airing cupboard There is a switch where you can move to see 3 different temperatures. marked SC, SR, SM Temp today at collector array showing according to read out 84c (SC) temp at solar storage vessel 22c (SR) and at midpoint 25c (SM) I would have thought that the temp would have been higher at SM rather than SR which is at the base. The 3 probes that are connected to the controller seem to be working ie: they are reading temps. Now here is a funny and found by accident, if I switch off the system by the isolator switch and leave off then switch on it puts the pump on for about a minute then switches off. While I was checking the system it did actually switch on its self but only again for a minute and switched out again. Checked water in system all ok, checked to see if there is any air in and no when bleeding water/feronox comes out. Showing a constant pressure of 1 Bar. The system is a sunuser and was serviced last year. Could the problem be the Resol controller?

[les]

As I said its a Resol and the model is E1/D

[les]

Getting closed now I have slipped out the probes from the middle and bottom of the tank and as soon as the temp dropped down by 5 degrees the pump switched on and stayed on, the water is now getting hotter. Have left for half an hour, put the probes back on and within 5 mins its switched off. This seems to me that it may be the controller as its not seeing the temp differential properly. On searching for the model have found a replacement but not quite identical, would probably use an electrician to replace it though.

it comes with new sensors. there are other here this sound like the controller to you?

[David Hansen]

On Sun, 31 May 2009 02:45:20 -0700 (PDT) someone who may be les wrote this:-

When you did that did the temperature of the panel go down and then steady? Did the pipes at the cylinder get hot? If so then the pump is pumping water around the circuit and transferring heat to the cylinder.

A basic differential controller. These days there is a lot to be said for a more advanced one with more features. is one supplier and the TDC2 would probably be suitable. I have not looked to see if it could use the same sensors, but I guess it could.

You shouldn't get that temperature difference with a working system, unless as I have implied there is something wrong with the controller settings. What is Tmax set at (using the terminology of )? Delta T?

Assuming the coil is in the bottom, the bottom will be hotter while there is output from the solar coil. When this ends the hotter water will move higher up.

If you take one out from the cylinder and hold it in your hand, then put it in cold water, does the indicated temperature change as expected? The same with the other one?

[David Hansen]

On Sun, 31 May 2009 03:42:27 -0700 (PDT) someone who may be les wrote this:-

What is that set too?

If you do not feel competent to do it then please use an electrician. The controller contains low voltage (230V) and extra low voltage (12V) terminals and mixing these up is not a good idea.

I would do a few more tests first before spending money on a new controller.

[les]

Yes the pipes and cylinder heated up and the temp dropped slightly and steady.

Thanks will look at that

Hmm getting into things I dont know about.

Reading was right then

I tested by wrapping it around with a cloth and holding a bag of frozen peas around it did this with both probes and they dropped in temp no problem.

[les]

Not sure, guess that would involve taking the controller off the wall as am not sure on this model where the settings are.

I would be more confident if the new one had terminals marked the same and it was just a swap out. However a local electrician has got to be cheaper than calling a solar engineer more than 100 miles away.

What further tests do you suggest that would rule the controller in or out of the equation ?

[les]

David you asked about the Tmax setting although the model is the same number as mine they have updated the model since mine was built some

22 years ago. There is no external Tmax setting on the one I have.

[David Hansen]

On Sun, 31 May 2009 08:26:15 -0700 (PDT) someone who may be les wrote this:-

I would leave it like that during the day and at least get hot water. At the moment the pump would probably be running all day anyway.

It does sound like the controller, as far as it is possible to tell remotely.

[cynic]

It could be, but before launching into a potentially expensive course of action you could try measuring the resistance of the cylinder probes using a half decent multimeter or ohm-meter. A damaged or failing probe might be causing confusion to the Resol Unit. Also possible is the Resol unit might have become garbled in its settings. I can't help you with your unit but Resol might be able to provide instructions as to clearing and reprogramming the settings. to avoid the heat your panel is absorbing going to waste you could, as a short term measure only, fit a flex and plug to the pump and run it continuously while the sun is out. At least the energy absorbed would be transferred to the cylinder that way.

[Dave Liquorice]

Indicates to me that the controller has got it's knickers in a twist. It must be possible to set the temperatures that things happen at. I suspect those settings have got corupted, anything from a power glitch to a cosmic ray flipping a bit in the memory.

I'd have a good dig about on the web for a manual or even have the covers off and a poke about. I'd probably not press a "reset" button unless I had already figured out how to alter the settings... Having said that the defaults may get the thing working properly again even if not at ideal settings for the size of you panels/tank.

There certainly doesn't appear to be anything wrong with the pump, the circulation, the pump switching, the sensors or the reading of them by the control unit. It's the logic that is playing up.

[les]

Well a bit of a suprise, had sent an email to the installer and they rang first thing.

1) rule out the pump force on as before and is the glass sight with float, is the float moving on pump start and should go up to a setting. Hmm never seen float but I know it must be vertical and above pump, so hunted around and under polystyrene found a glass sight and yep its pumping and liquid in. 2) Controller pull off and check what is the temp diferential dial set to, 2-11. It was set at the very lowest 2, should be set to 6. Now ever since we moved in here 3 years ago the solar system has not switched on all day so we presumed that it was correct, the service we had was a refill of antifreeze and no one has touched the controller. I see from the old invoices that a full service was done 5 years after instal so that would be in 1993-4 so was the controller set wrongly then or has it ever been set - Or have one of the previous owners fiddled with it, I did note that on removing one of the bolt holes (plastic) were broken, cant see installers doing that.

Now I have to feedback tonight.

On plugging in the controller this time and switching on its been on so far 3 hours and temp to tank has risen from 22c to 40c so am hopeful. Also the installers said they could supply me with a new unit that they could post out and I could just plug in so no need for a visit.

Wow for the first time are we actually gonna get HOT water.

Will let you know what transpires.

[David Hansen]

On Mon, 1 Jun 2009 03:06:58 -0700 (PDT) someone who may be les wrote this:-

Glad you seem to have found out what the problem was. That setting is what in the manual you found is called delta T.

Thanks.

[Jules]

You'd be surprised... :-)

[les]

Seems now to be working correctly temp got up to 71c in tank and has turned off the pump so got lots of hot water now. Been talking to the neighbours and they knew the original couple who had it put in, in 1988 and outwardly they were saying how wonderful the system was, they were agents for the company but to their friends they were saying they were not very impressed as the water didnt reach bath water temp. WHY DIDNT THEY SAY!!!!

Anyway its fixed now, strange how the company didnt pick this up since then but if the couple were sayings its ok why should they!!!

It just happens for me that it was ideal testing time as the last few days the weather has been constant and good and Ive been off work, not often that happens hey?

Thanks to all who helped me reach this point.