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Seven steps for servicing your solar thermal system

Posted by Paul Hutchens on 19 March 2010 at 10:09 am

How to service a solar thermal system is a really common question asked by many of our customers and prospective customers. Unfortunately there isn't really a definitive answer. It depends on how technically minded you are and how much peace of mind you need. So here are some guidelines:

1. Solar thermal heating systems are low maintenance systems which require little regular planned servicing. The only moving part is the pump which is a relatively low cost item (less than £100) and reasonably easy to change. The electronic controllers sometimes fail, albeit rarely, and these are also reasonably inexpensive and easy to change.

2. Keep an eye on your system. The main thing to watch out for is fluid leaks – especially the antifreeze which smells rather strong. If there is a leak contact your installer.

3. Make sure your solar system is doing what you expect. If the weather is sunny and your hot water cylinder is cold you may wish to look a bit deeper – unless of course you have just enjoyed a deep, relaxing bath!

4. Similarly if the pump is running but the solar pipework is cold you may have an airlock which your installer can sort out for you.

5. One thing you may wish to look at from time to time (say once a month) is the pressure of the system which should between 1 and 2 bar – although it can drop as low as 0.5 bar in cold weather as the fluid contracts and as high as 3 or 4 bar if the system gets very hot. This is nothing to worry about but if the system falls below 0.5 bar and stays there, contact your installer.

6. The antifreeze in your system will degrade over time and need replacing eventually. However bear in mind that the antifreeze is designed to cope with temperatures as low as -28C; the coldest temperature ever recorded in the UK is -27C and that was before climate change. So the system should be fine for at least 10 years. One of our suppliers installed a system at his house in the north-east of England in the late 1970s and has never needed to change the antifreeze.

7. If you want peace of mind, installers like us will perform an annual service to check everything is working as it should.

I hope that this helps and that you get years of free energy from your solar thermal system.

Photo by Elsie esq.

About the author: Paul Hutchens is founder and director of Eco2Solar, which installs solar systems around the UK.

If you have a question about anything in the above blog, please ask it in the comments section below.

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13 comments - read them below or add one


selenakaleComment left on: 29 October 2020 at 2:26 am

I have learned about it but not much, thanks for your information


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npgarwoodComment left on: 9 January 2020 at 6:36 pm

I have had solar thermal for nearly 10 years now, but the pressure has dropped to zero for the 2nd time this month (last time in 2015). Three questions

1. How easy is it to recharge myself?

2. Is it possible/cost effective to change the system to a non pressurised system?

3. What happens if I don't get the system re-pressurised. It is still heating the water ok?

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Carole Gannon

Carole GannonComment left on: 11 August 2019 at 6:55 am

Does anyone know of a company that services PV-T panels? Mine were installed in 2012 by a company which has now gone out of business.  I live between Portsmouth and Chichester.  Any help would be appreciated.

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EtypejagComment left on: 16 January 2018 at 3:29 am

Can somebody tell me why I have to give evidence of ownership for having a solar water heating panel on my roof. The system was installed when I had my boiler replaced for a combi back in 2009. Now I'm selling my house the panel has become a sticking point because the solicitor needs evidence of ownership and I do not have documentation either.

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Paul Hutchens

Paul Hutchens from Eco2SolarComment left on: 21 December 2017 at 5:10 pm

Hi Keith

Seconsolar in Sunderland supply antifreeze. It comes ready mixed or 40% Glycol with water.

It is available elsewhere but make certain it is the correct glycol for solar thermal systems.


Kind regards


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bucklnwrComment left on: 21 December 2017 at 4:25 pm

Dear Paul.

My system requires the Antifreeze solution (Glycol?) topping up.  Where can I source this and what concentration do I need.  In the North Worcestershire area.


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Paul Hutchens

Paul Hutchens from Eco2SolarComment left on: 8 February 2016 at 1:06 pm

Dear Ann

We recommend a heating engineer who used to work for us installing solar thermal for servicing work.

His name is Ben Fox and his telephone number is 07918 828385 or email

I hope this helps.

KInd regards


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Ann Wright

Ann WrightComment left on: 6 February 2016 at 2:48 pm

Finding anyone to service my Thermal Solar system when the installer went out of business long ago, has proved to be a nightmare. Cold calls claiming to have taken over my installer.... all claiming different frequency times for servicing. Some saying Two to three years others every year and all quoting a different cost. I live in Warwckshire and would very much apreciate the honest truth and someone to give my system the correct service that it needs.

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Cathy Debenham

Cathy DebenhamComment left on: 7 May 2013 at 8:30 am

Hi Phil

Sorry to hear you've had a bad experience. If you click here and select solar thermal and London, there are some very good companies listed who will certainly be able to help with solar thermal, and may well be able to do more than that.

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Phil Gough

Phil GoughComment left on: 3 May 2013 at 5:11 pm

I had my thermal heating installed along with a new central heating system (with unvented tank) in 2008, I was unable to find a single contractor to do both installations,  I employed a company Ecologistics in north London who shortly after walked away from the solar thermal business and no longer wanted to know anything to do with supporting their customers.

The consequence is that now I have to employ three contractors to look after the system: for the solar part, for the boiler and radiators, and for the pressure vessel testing. All this is expensive and inefficient.

Are there any contractors in the NW London or Herts area who can do a "one stop shop" operation for these tasks?  I am particularly keen to find somone to support the solar thermal part when needed.



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NicoleYouGenComment left on: 19 April 2013 at 10:12 am

Hi, Deb Russ, If you have not yet looked, you can try looking through our directory for companies installing solar thermal in Kent and ask around. I just did a seach and found 10 local companies in Kent and 184 companies that work in Kent, so someone is bound to help! You can look at the reviews and contact the companies through our directory. Good luck!

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Deb Russ

Deb RussComment left on: 18 April 2013 at 6:40 pm

I am looking for a Kent based company that will come and service a solar water heating system that has been installed for about 7 years. Can anyone recommend a company who will service a system that they did not install?

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Jayhawk International Ltd

Jayhawk International LtdComment left on: 3 May 2010 at 2:40 pm

As Paul expressed in the above Blog, solar thermal is supposed to be simple and not requiring as far as I am concerned after 18 years in solar collector design and system design any servicing at all, except checking the controller is switching the pump off and on and the pump works, no different to a vented boiler with a header tank and 3 port valve.

As always when something is simple and very rarly goes wrong is when the corparate companies and the big manufactures start to look at adding in added value.

Not coming from the plumbing and heating industry, but ended up becoming very involved in that industry for 35 years across all sectors, what I have always done in my business life is do what Salmon do when looking to swim against the tide to their spawning grounds.

Many plumbers and DIY installers I have educated and trained over the years through a renewables distribution business I closed down last April still contact me today to tell me how efficent the solar water heating system they purchased from that business was and glad they had followed my installation direction, not that the industry is going down through the MCS route.

Our new approach both inside and outside MCS will be to promote open vented solar water heating systems even when the cylinder is unvented.

The first proven aspect about this system, is that 50% of the componants being added into kits will no longer be required.

Secondly, the installer will have less call outs becouse of falling pressure in the closed loop, demonstrated by the Gauges located on pump stations.When the plumber/installer is called back, it comes out of his profit along with losing another days work.

Thirdly, what the home owner does not want and I can gurantee if they knew what to expect in proposed service charges etc, will no go ahead with a solar water heating installation.

Our full range of new Thermaltricty hot water and space heating systems will be service free, guranteed for 5 years when our innovative method of installation is followed.

Many imported vacumm and flat plate will not be suited to these installation types I have designed, becouse of the need to displace the air in the many U bends of copper pipes in the collector and the overheating with CPC types when the unvented water tank, shuts the controller down, thus decreasing the time scale when the Gylcol needs to be replaced.

Eric Hawkins (designer)


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