Solar hot water system issues

In my particular case, the installer failed to install a downpipe on the blowoff valve to keep the boiling water off the colorbond roof. As a result, the iron has corroded through and will soon begin to leak into the house. The gutter and downpipe have also corroded away. When the same installer came to service the system, he failed to mention this or to remedy the problem. He also, at the time of the original installation, failed to install insulation to prevent the hot water system freezing up at night. When recalled to rectify the problem, he simply covered exposed sections in old polystyrene fish boxes which were fully exposed to the weather.

Welcome to the community Kerry.

How did you find this out?
How should this be done? Wouldn’t a PVC pipe not melt, and a metal pipe corrode away like your downpipe etc.?

Is this directly attributable to the water coming out of the blowoff valve, or is it an evironmental issue such as living near the ocean or other corrosion source?

Are you absolutely certain they are old fish boxes, or do they just look like old fish boxes?


Hi @Kermac, welcome to the community.

Many solar hot water systems have freeze prevention designed into the system. When the temperature of the panels decreases to near freezing, water from the storage tank is recirculated through the pipework and panel to prevent freezing (and bursting of the pipes/panel).

The storage tank which holds the water will also be insulated to reduce temperature drop when the ambient temperature is less than that of the stored water.

Generally enclosing of pipes or system isn’t required as most solar hot water system have their own protection in place to prevent damage from freezing. If you lived in some of the coldest areas of Australia (at altitude or say in Tasmania), insulation may be useful not only to prevent pipe freezing, but to increase the efficiency of the system (heat loss is less).

Notwithstanding this, during times where the protection is operating, if it is at night it may cause the booster heater to operate resulting in increased electricity/gas use.

This sounds like a water quality issue. You town water may be higher in ions (inc. salts) or acidic which can cause accelerated corrosion of metals. I haven’t heard of special stormwater pipes being installed to prevent pressure release water not coming into contact with roofing or guttering. Doing such work wouldn’t look attractive (pipes overhanging gutters) and/or in the long term may be a source of leaks within the residence (if holes are made in the roof to internally plumb away any water).

If it is high in ions/acidic town water you are on, it will be extremely important to have the system serviced regularly as the internal cathode is like to dissolve quickly reducing the life of the storage tank. I would be asking the installer/manufacturer their recommended service and cathode replacement intervals in a corrosive water environment.

There is also an Australian Standard

which deals with the installation of solar hot water systems. This is the standard that licensed tradies should be using as a minimum for such installations. This is usually reflected in the installation guide for a solar hot water system. I don’t have access to these standards, but it may worth checking the manufacturer’s installation guide about the recommended installation and whether it shows that the guide complied with the Australian Standard.

Edit: Thinking further, if it is iron stain on your Colorbond roof, this won’t be corrosion of the Colourbond as it is made from magnesium, aluminium and zinc compounds. One of these produce a rusty stain. If you have iron staining and have galvanised pipes within the house or to the street mains supply, it could indicate that the galvanised pipes are rusting…hence a rusty stain building up on the roof.

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First question: the downpipe. A friend sent me a copy of the relevant pages of the Owners Manual which includes installation instructions (evidently I was supposed to receive a copy at the time of installation, but didn’t). On the subject of drain lines, the manual says: “The TPR valve and ECV should both have drain pipes connected to their outlets. These pipes should run to ground level where hot water discharge is safe… Do not allow water from the valve outlets or drain pipes to drip or discharge onto roofing materials or roof gutters”. In addition, “As the function of the TPR on this water heater is to discharge high temperature water under certain conditions, it is strongly recommended the pipe work downstream of the TPR valve be capable of carrying water exceeding 93 deg C. Failure to observe this precaution may result in damage to pipe work and property”.

Q2: An environmental issue? - No, the house is located well inland (southwest slopes and plains) and there is no corrosion source nearby. The corrosion begins directly under where the drain pipe spills onto the colorbond roof (or where it used to spill until the Solahart plumber moved it a few centimetres so it now runs down a different channel in the roofing iron. There is no sign of corrosion in the new location yet - but it has been only a year since the pipe was moved).

Q3: Freezing at night - I assumed the system had some freeze protection built in, but during the winter following the installation, the hot water pipes froze solid for the first time ever (we had been living there approx.6 years). I initially requested a split system so the hot water was pumped into a tank inside the house where the rate of heat loss would be much less than it was sitting on top of the roof through our freezing nights. The plumber talked me out of it saying it was “too complicated”, but I suspected at the time he had never done one of these installations.

Q4: Corrosion and water quality. Undoubtedly this is related to the mineral content of the town water (which tastes too foul to drink, make tea or cook with). However, the other pipes in the house (around 40 years old) do not appear to have suffered from corrosion (eg reduced water pressure), and as soon as the pipes had insulation applied the problem never recurred.
The system operated quite normally for around 8 years before it began to fail, in spite of no service being carried out (the need for service never having been brought to our attention). I’d have to check whether the cathode was replaced when serviced last year.

Q5 (Edit): Corrosion of colorbond - The corrosion has eaten clean through the colorbond paint finish to the metal beneath, and has begun to rust through the metal itself. I have discussed this with BluSteel, manufacturers of colorbond, and once the corrosion is removed and neutralised, it can be painted over with specific paint products. However, they advised me to prevent boiling, mineral-rich water being run down the roofing iron again, preferably by means of a pipe.
At this stage I’m still not sure whether this can be done or whether the entire sheet of roofing iron will need to be replaced. THis would involve dismantling the Solahart heater and removing it from the roof in order to get the new sheet underneath. This would be a major operation, probably both difficult and expensive.

Q6: The old fishboxes used to provide insulation - There are no markings on the polystyrene, but they certainly resemble fishboxes. After 8 years in the weather they are certainly old, and disintegrating. They are loosely strapped to the roof in a very makeshift way, and were clearly not designed for this purpose. I assume they are covering pipes or something that is prone to freezing. Up close, they look very amateurish

It could also be Colorbond issue and not an installation issue. As BluSteel have recommended piping the water away, it appears that they may be aware that their Colorbond product isn’t suited for installation of solar hot water systems which discharge ‘mineral-rich’ water onto the roof. Piping water away may not be part of a standard installation and the installer may not be responsible for the issue you are facing.

It is worth noting that temperature will only have an effect of accelerating the rate of oxidisation of the roofing…colder water won’t prevent oxidisation if they believe ‘mineral-rich’ water is the source of the issue.

It also appears that your system is a minimum 8 years old. As the installation is old, it will not only fall outside the Australian Consumer Law as well as any building defect period. Most defect periods are up to 7 years where they apply (based on the type of work and it’s value).

It is also unlikely to fall under home insurance, but it may be worth exploring if the costs to fix mount up.

It may be worth speaking to a rooking expert in relation to what solutions are available. Also ask if it possible to install a patch rather than a full sheet. A patch may be the cheapest option.

A patch being where they cut out the affected area and install a new piece of roofing (rather than a full sheet).

The manufacturer of your system (brand or model would be useful) would have provided an installation manual/guide with the product. The installer may have kept it, and as you note you have needed to source an owners manual. Some are a single document. Most are searchable online. There will be instructions and recommendations for installation of your model in areas subject to freezing conditions, assuming the model was suitable for your site.

There are insulation kits and standard piping insulation products available through the plumbing supply wholesalers. These include products which are UV stable and suitable for external installation. Bare polystyrene is not UV stable, although it can be wrapped, coated or protected by a product that is. There are plumbing services that have the staff able to carry out roof sheeting and solar HWS piping p/insulation, if you see a benefit of one provider rather than arranging for the work independently?

Have you discussed the issues with the supplier?
Alternately most of the major brands have customer support services you might contact directly.

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