SOLAR WATER HEATING SYSTEM PROBLEM - CONFUSED!

X20DTL

Looking for some help with my solar system problem.
I have a 2-panel (flat panels) system which lately seems to struggle to get the tank (200L) up to 50 celcius even on the best of sunny days.
I have noticed that it seems to charge the tank Ok up to this point but after that is simply cannot transfer the heat from the panel to the tank and subsequently the panel rise above the 110C limit and the controller then circulates no more.
I have noticed lately that there now seems to be air in the system however the gauge still reads just under 3BAR.
I bled some air from the pumping station and on the flow/return of the lower coil going into the tank but it seems to get air locked again.
i don't believe i have a leak as the pressure would be falling however there is still air in the system.
I wonder is the circulation pump on the way out? Would the pump be good enough while the fluid is not too hot i.e. under 50C but as the system heats up that it loses efficiency and simply cannot pump up to the panels?
One other factor that might not be helping it is the pump is a 3-4meter Wilo unit however my panels are on the roof of my 2-storey house but the pumping station and tank are on the ground floor, maybe the pump is'nt good enough for the height distance to pump any longer?
Lastly, the sensors & control panel seem to be working as it circulates perfectly normally until you get near 50C so the problem must be somewhere else.
Could a failing pump churn the fluid in the circuit and liberate gas/oxygen from the fluid?
It's really confusing to think it's getting airlocked but there doesn't appear to be a leak anywhere.
Any ideas out there as to what might be the problem?

John

air

There's air in the system, you need to bleed it when it's cold and get it back up to pressure.
You must have a leak somewhere.
Is there much variation in the pressure shown on the gauge between day and night?

X20DTL

air wrote: »

There's air in the system, you need to bleed it when it's cold and get it back up to pressure.
You must have a leak somewhere.
Is there much variation in the pressure shown on the gauge between day and night?

There's no pressure diff between day & night or at least so small a difference that it's not noticeable.
Could a failing pump churn the fluid causing cavitation or other that might cause a liberation of gas or air from the fluid? I'm thinking not but worth asking anyway.
If I have a leak wouldn't the pressure slowly fall over a few weeks or so?
The pressure is not falling as I've been watching it for a few months now and not a stir.
It will obviously drop when I bleed it but if I never cracked a bleed valve open then it will not fall.
Any chance it could be the pump?

air

Is there a flow meter in the pump station that you could look at?
Can you crack open the circuit and redirect to a container for a second or two to see if it's pumping?
It can't be circulating properly if it's stagnating and shutting down on high temp.

X20DTL

air wrote: »

Is there a flow meter in the pump station that you could look at?
Can you crack open the circuit and redirect to a container for a second or two to see if it's pumping?
It can't be circulating properly if it's stagnating and shutting down on high temp.

Yes there is a flow meter just below the pump on the suction side. When the controller kicks the pump in, the float in the meter lifts up to about 3 litres per minute so does appear to be circulating.
What's really confusing me is the air present in the system which would indicate a leak but I'm not getting a pressure drop, this is what's really baffling me!
The pressure staying static tells me the system is not breached so is the air being liberated from the fluid?

air

I don't think that a circulation pump turns fast enough to cause cavitation.
Are you in a hard water area? I suspect that your solar coil may be calcified reducing the heat transfer to the tank. This would explain the low temperature & early stagnation.
Did you ever look at the flow meter while it was working normally.

X20DTL

air wrote: »

I don't think that a circulation pump turns fast enough to cause cavitation.
Are you in a hard water area? I suspect that your solar coil may be calcified reducing the heat transfer to the tank. This would explain the low temperature & early stagnation.
Did you ever look at the flow meter while it was working normally.

Yeah, I agree about the pump & cavitation but it was the only thing I could think of! :-(
Yes, I'm in a hard water area and had initially thought the same thing about the coil being coated with scale but it wouldn't explain the air in the closed circuit between the panels and the tank. I have read on the net that a few gallons of vinegar left over a weekend in the tank of water will dissolve the lime scale on the coil.
What if I drained out the circuit and refilled it with fresh glycol mix & bled the air out of it?
I'm guessing that whatever contractor could do it would be able to detect a leak if there was one, right?
The trick is to get a decent contractor which may not be so easy.

air

X20DTL wrote: »

Yeah, I agree about the pump & cavitation but it was the only thing I could think of! :-(
Yes, I'm in a hard water area and had initially thought the same thing about the coil being coated with scale but it wouldn't explain the air in the closed circuit between the panels and the tank. I have read on the net that a few gallons of vinegar left over a weekend in the tank of water will dissolve the lime scale on the coil.
What if I drained out the circuit and refilled it with fresh glycol mix & bled the air out of it?
I'm guessing that whatever contractor could do it would be able to detect a leak if there was one, right?
The trick is to get a decent contractor which may not be so easy.

Is there definitely a continuous buildup of air in the system?

X20DTL

air wrote: »

Is there definitely a continuous buildup of air in the system?

Yes, there would appear to be. Are you thinking that the expansion vessel might be charging the glycol circuit with air?