Solar Water Heating Failure

[TheFew]

Hi,

I am looking for some guidance with my latest domestic problem, which is this time... my solar water heating.

When I bought the house it had solar water heating pre-installed. This consists of three panels on the roof that are operated by a "Worcester" unit in the loft and feeding two hot water tanks in the airing cupboard that is monitored by a "Worcester" TDS10 control unit.

The solar water heating has been working fine over the last few weeks, however a couple of days ago it suddenly stopped producing hot water.

Looking in the loft, the system pressure seems to have dropped to zero. However I am not sure if the pressure should always be at the set "red line" level even when the pump is not working (I guess it probably should be, as this is the case with my central heating). Looking at the system in the loft there seems to be a pressure relief valve that vents system fluid into a blue plastic drum (presumably when the pressure gets dangerously high), however this drum is empty, so no fluid has been vented here.

The TDS10 control unit still shows a animation of fluid cycling around the system, however the tank temperature is not increasing. Also the wife has reported that it has flashed up with the error "SYS" from time to time.

So the question is... how do I diagnose and repair the fault? I know next to nothing about the system, and I'm looking forward to learning!

Thanks

 

[PlacidCasual]

Is there a filling loop like on an unvented boiler system? If so you could try re-establishing the pressure and seeing how quickly it decays, it might inform you if there is a leak. Are there any isolation valves between the different legs of the solar panels (are they in parallel or series) and if so can you isolate one then the other whilst doing you pressure test to remove one from the equation. Just my suggestions as a mechanical engineer not a home heating technician.

 

[TheFew]

Hi, I am not sure if there is a filling loop or not (I will have to go check). For some reason I am assumed that the system would not be filled with water, but with something else that has a higher boiling point as the panel temperatures can reach 130 deg C (if the control unit is to be believed).

Re if the panels are in parallel or is series.... in the loft there is one pipe that goes to the panels and one what returns so I presume this means that the panels are in series.

 

[The Artfull Bodger]

It's filled with glycol and filled using an external pump, get a plumber who does solar.

 

[TheFew]

I feared that would be the case. I was hoping to sort it myself due to financial pressures, but it sounds like it is well outside my abilities

 

[TheFew]

So as mentioned above the system is showing zero pressure.

To get some how water I have tried using the electric immersion heater backup and also the main gas boiler. As a result we now have hot water again, but the TDS10 control unit still only shows a tank temperature of 29deg C.

Is it possible that the TDS10 control unit failed first and as a result caused the solar water heating system to lose its pressure? What would be the failure mode/series of events?

I am guessing I need a new control unit or temperature sensor too?

 

[The Artfull Bodger]

Loss of pressure can only really happen from a leak/seap over time or temperature-pressure-expansion vessel failure/loss of charge causing the safety relief valve to discharge or loss of pressure. You should still be able to get hot water from the boiler which is always the primary source. The solar should only kick in and stop the boiler firing when the delta from the fluid temp and hot water cylinder is high enough and stop if the solar temp exceeds 110 or whatever it has been set up for. Read the controls literature and try to turn the solar side off to rule out this interfering with hot water if your having issues warming the tank. Or get an engineer round to diagnose/rectify, please be aware that solar can be dangerous with regards to the heat, as you've noticed it can get hot I've seen temps on controls showing over 150 c.

 

[ron3003]

Pressing the top button on the TDS10 will cycle through the temperature sensors at various points on the system. Default display is bottom of tank so 29c would be about right . Next press is the top of tank sensor which is where any hot (60c or thereabouts) water available will be and next press is the solar collector panel manifold temp. If you've seen 130c at the manifold then the system has stagnated and boiled possibly due to pump failure or an undiscovered leak allowing an airlock to prevent circulation.
Is the pump working? Pull the polystyrene cover off the pump station, it's only for insulation. Behind is the pump which you should be able to hear. There should be a sight glass (flow meter) with a small ball which rises with the solar fluid flow. If it's at the bottom the fluids not circulating.
That blue drum is a bodge and most certainly not rated to survive an escape of superheated water past the pressure relief valve.

 

[TheFew]

Hi,

My TDS10 only shows two temperatures. Panel temp (120 deg) and bottom of the tank (29 deg). There is no installed sensor at the top of the tank. The wife is sure she has seen the tank sensor display higher temps and hence the assumption it is not working...

Re the pump, it is making a noise (kind of a whirring). The inspection glass (labelled l/min) has no sign of fluid in it and no sign of a ball. So given the pressure is zero I presume there is no circulation. I decided to remove the power to the pump for now as it seems pointless leaving if powered with no water moving.

Engineer visit booked, but they cannot come until the 14th. What is the worse that can happen before then????

PS. I was also surprised by the drum bodge, but where would you normally vent superheated liquid too? A normal overflow pipe to the outside of the house sounds pretty dangerous too!!

 

[The Artfull Bodger]

The glycol container was an accepted method in the old days, now a days your meant to have a proper discharge container with high temp rated plastic. While not to current standards, when installing in the past, if I over pressurised the system I used the relief valve (not recommended with valves that aren't new as they may not reseat) to lower the pressure in the mid day summer sun - the glycol containers never showed any signs of melting/warping. Speak to the engineer when he arrives if your worried.

 

[TheFew]

It did discharge to that container about 2 years ago and it seemed OK...

 

[TheFew]

So the solar engineer turned up for 30 mins. A quick look for leaks (none obvious) and a pump up of the expansion tank (no pressure present) to 2.5bar (it took pressure) and the diagnosis is.... The glycol has probably just evaporated. So that is £80 for that visit and a further estimate of £180 plus VAT to come back and recharge the system with glycol.

So not sure if it is worth the effort...

After he left I could hear the expansion tank ticking.. Perhaps the applied pressure escaping the diagphram?

 

[TheFew]

Still a ticking noise from the expansion tank 2.5 hours after the engineer left. So I guess it is loosing air.

So with a new expansion tank the cost will be £360. Is it worth the investment? My house (an old B&B) has two 180L tanks. Or would just using gas in the cold months and an electric immersion in the warm months be cheaper?

 

[Dangerous Dave]

Looks like it is not worth it, I heat a 300L hot water tank for 45-50p a day in gas through the summer. Electric immersion heaters are far more expensive to run compared to gas as electricity is 4x the cost per kwh compared to mains gas.

Have you looked at filling back up yourself ? Glycol is available online

 

[Kimi]

Put some washing up liquid on the air valve of the expansion tank and see if it's leaking air through the valve. If it is that's a 50p fix. They use same valves as bikes, If the diaphragm is leaking in the expansion tank then you could replace the tank yourself to save some money.

 

[ron3003]

Solar Fluid doesn't just disappear, if it's not in the blue bucket then it's vented out as steam somewhere in the closed loop.
Main suspect is usually any automatic air bleed valves not rated for solar temps that the installers fitted. These should be at the highest point of the system so in the roofspace or adjacent to the solar panel/tubes.

 

[TheFew]

Looks like it is not worth it, I heat a 300L hot water tank for 45-50p a day in gas through the summer. Electric immersion heaters are far more expensive to run compared to gas as electricity is 4x the cost per kwh compared to mains gas.

Have you looked at filling back up yourself ? Glycol is available online

In the summer I tend to turn the boiler off into frost protect mode, so I guess to use the boiler for hot water creation I would have to keep the core boiler temperature at a more reasonable level all year.

Having just had a look online refilling the system does not look too bad if I can work out what is what on the system. It does look like I will need to but some form of pump to insert the fluid however. And the another pump to charge the expansion vessel.

 

[TheFew]

Put some washing up liquid on the air valve of the expansion tank and see if it's leaking air through the valve. If it is that's a 50p fix. They use same valves as bikes, If the diaphragm is leaking in the expansion tank then you could replace the tank yourself to save some money.

Will do. I learnt that the valve is at the bottom of the tank. I will also grab a cheap pressure gauge to check the tanks pressure. The noise I heard sounded like it was coming from the middle of the tank, not the bottom however.

 

[TheFew]

Solar Fluid doesn't just disappear, if it's not in the blue bucket then it's vented out as steam somewhere in the closed loop.
Main suspect is usually any automatic air bleed valves not rated for solar temps that the installers fitted. These should be at the highest point of the system so in the roofspace or adjacent to the solar panel/tubes.

Thanks I will look for these. I can't easily reach the panels on the roof but can check the roof space. Even though the expansion vessel was low on pressure the fluid was not hiding there, so it had escaped somewhere else.

 

[Foghorn Leghorn]

So the solar engineer turned up for 30 mins. A quick look for leaks (none obvious) and a pump up of the expansion tank (no pressure present) to 2.5bar (it took pressure) and the diagnosis is.... The glycol has probably just evaporated. So that is £80 for that visit and a further estimate of £180 plus VAT to come back and recharge the system with glycol.

So not sure if it is worth the effort...

After he left I could hear the expansion tank ticking.. Perhaps the applied pressure escaping the diagphram?

Good grief, find another 'engineer', fluid cannot evaporate from a closed system.