Solar tubes problem

unkel · 23-07-2019 11:23pm #1

My 40 tube Kingspan HP400 Thermomax system, installed November 2016 has not been working well the last few months. First I got an error message on the SC400 controller, then performance was down and then it did about nothing

According to my SEAI installer, it could be a number of different things, like a coolant leak or an air bubble. He promised a full service, changing the coolant, will sort this. €250 for that including a special leak sealant agent. They weren't keen on just an inspection, full service or nothing really. Not really what I was hoping for as the main reason I went for the Thermomax system is that it vents itself at 95C, so the system is much simpler and safer, doesn't need any heat dump and the coolant should last a long time. I know these systems need servicing, but I was rather hoping for a 5 year or so interval, not 2-3 years

Was about to agree to have it serviced this week until I checked the system today (we're just back from a near 2 week holiday) and to my great surprise the system was working very well. With the bottom of our 360l cylinder very quickly to 60C after all the family members had fairly long showers throughout the day. I know it was a warm sunny day, but still. Full tank is at 60C now (close to the maximum setting of 63C iirc)

Anyone any ideas of what happened here? Or was it just a bit of a fluke and my system will be jammed again soon? For the moment I'm holding off on a service.

quentingargan · 24-07-2019 9:58am

If there is air in the system, you will get noise when the pump is running. Is there a lot of gurgling?

Any change in the system pressure?

When the system was down, what were the temperature readings at the panel? Often, a poor connection to the panel probe will cause the system not to pump. If the panel is reading hotter than the bottom of the cylinder, the pump should run. Hard do diagnose all that now while the system is running.

Do you remember what the error message was? I don't think a controller error message would be caused by an air lock

unkel · 24-07-2019 11:47am

I haven't heard any gurgling. I took attached two pictures (apologies for poor quality) last month when the system was not heating water at all. No error codes on the controller and all temp sensors appeared to be indicating the correct temperatures (on the tubes, on the top of cylinder and on the bottom of cylinder). The funny thing was that the number of hours shown on the controller was increasing, but maybe that's only an indication of the number of hours that the tube temperature was more than 8C higher than the bottom temperature and has nothing to do with the actual hours the pump was running?

quentingargan · 24-07-2019 12:34pm

Well, presssure has dropped which could either be a leak or a failed expansion vessel. Since there is no gurgling, it might just want pumping (there is a bicycle pump fitting under the black cap at the air side of the expansion vessel).

I am not an expert on the Kingspan system, but I assume it has a blow off valve. This might have blown off once for some reason, but this might be a symptom rather than the cause of problem you had, which could be any one of a load of things - poor connection to temperature sensor, pump temporarily seized or failed for some other reason. If you are going to the expense of having it serviced, I would be tempted to wait a while to see if it fails again so that the installer can diagnose the problem while it has failed.

unkel · 24-07-2019 12:59pm

I asked the installer and they have been installing about 500 systems a year if I understood him correctly and they've only ever have had 2 pump failures. So he was adamant it is extremely unlikely it's the pump. The green led light on the pump is on too. I'll have a look at the pressure again later. What should it be in a healthy system, about 1 bar?

Good to know about the bicycle pump fitting. I don't really understand what it does though? Can I safely pump for a bit when the system will go bad again?

quentingargan · 24-07-2019 1:07pm

The water in the system is to expand and contract. The expansion vessel has a diaphragm across the middle with air on one side which allows the expansion. This should have been pumped to the presssure in the system. If it isn't, then when the volume of the side with air reduces when the system is filled as the air compresses. That reduces expansion space so if the pump is stopped and water heats up, you may get some water blown off as there is too little air. The system still requires a service.

Your system currently has 1/2 bar of pressure and looks like it originally had 2 bar. You could see if the pressure fluctuates much between night and day.

You sound like you have an experienced installer and they would know better. True, pump stations seldom fail. However, i have seen probes fail, or have their connections damaged in the loft area.

spose · 25-07-2019 8:02pm

I’ve had that issue with probe as well. It got a bit of a knock and was reading 160c on the bottom of the tank so never called for pump to turn on. A jiggle of the probe and went back to normal. You should be able to see the total number of hours pump has been running. If you track that for a few days then you’ll see if it’s not running

unkel · 25-07-2019 8:12pm

The temp probes all show the correct temps in the controller. The number of hours on the controller is going up. But that might just be a software indicator of the number of hours that the temp delta has been positive. Might have nothing to do with the actual hours the pump has been pumping and even if it did, the performance of the system could be negligent

Had another look at the pump a couple of hours ago. AT the pump, the hose coming from the tubes is burning hot. The hose going to the tubes is cold. Their is a temp gauge on both and the incomer is 60C and the outgoer 20C which feels about right. Pressure is 0.5 bar (far too low) and the flow indicator shows 4-6l per minute, which seems far too low too. There is some performance, but minimal. I guess it is time to book in that service afterall.

quentingargan · 25-07-2019 9:24pm

unkel wrote: »

Their is a temp gauge on both and the incomer is 60C and the outgoer 20C which feels about right. Pressure is 0.5 bar (far too low) and the flow indicator shows 4-6l per minute, which seems far too low too. There is some performance, but minimal. I guess it is time to book in that service afterall.

The flow rate should be good enough to keep the temperature differential at less than about 10 degrees. If your panel and incomer is at 60 and the tank is at 20, the flow rate is way too slow. That could well be air in the system.

Get the service, but I still think you should check that expansion vessel and see if it caused the problem in the first place.

unkel · 25-07-2019 9:37pm

quentingargan wrote: »

I still think you should check that expansion vessel and see if it caused the problem in the first place.

Not sure how I can check it? It seems to be empty, when I shake it, I hear nothing.

quentingargan · 25-07-2019 9:39pm

unkel wrote: »

Not sure how I can check it? It seems to be empty, when I shake it, I hear nothing.

It should be half full of water, but with your pressure so low, I doubt if it is. When the system is drained, the installer can pump it and see if it is holding pressure.

unkel · 25-07-2019 9:40pm

Pretty sure it's empty. Nothing left for me to try then, Quentin? Just book the service?

Much appreciate all your help BTW

quentingargan · 25-07-2019 9:42pm

unkel wrote: »

Pretty sure it's empty. Nothing left for me to try then, Quentin? Just book the service?

Much appreciate all your help BTW

Defo shouldn't be empty. You need a plumber alright.

unkel · 25-07-2019 9:49pm

I'll book in the service so.

bunderoon · 03-08-2019 4:39pm

unkel wrote: »

I'll book in the service so.

How did you get on with the issue?
Was looking at the make/model of yours instead of a heat dump but if you've spotted a weakness in their system, it would be good to know.

unkel · 03-08-2019 9:49pm

bunderoon wrote: »

How did you get on with the issue?
Was looking at the make/model of yours instead of a heat dump but if you've spotted a weakness in their system, it would be good to know.

Booked it in for a service.

I don't think there is a weakness in this system, I have checked with Kingspan and they officially recommend an annual service. Which seems a bit crazy to me, i.e. if you compare to a car, you only change the coolant every 3 years or so and that coolant is not only under pressure, but gets far hotter than the max 95C this system gets. My system has been up for nearly 3 years now. I guess my expectation was that it would only need a service (to change the fluid) every 5 years or so. Bit disappointing that it looks more like every 2-3 years.

I'll update here after the service.

unkel · 11-08-2019 8:25pm

System was serviced Friday. Engineer found a leak. Probably caused by ourselves moving boxes around in the attic storage area. He replaced all coolant and added a container of leak sealant. He said the pressure is now up to 2.5 bar. The "old" coolant still looked pretty fresh to me. I'd say you'd be fine to change it only every 5 years with this system that doesn't go over 95C, as I had hoped to start with. I'd rather not spend €250 every 2 years!

quentingargan · 11-08-2019 9:03pm

I'd say you'd be fine to change it only every 5 years with this system that doesn't go over 95C, as I had hoped to start with. I'd rather not spend €250 every 2 years!

Thats good. It is stagnation and bringing glycol up to 140C that does the damage. A service every two years would poke a big hole in the payback calcs...

Solar tubes problem

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