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Thread: Fitting hot water kit thermostat to OSO Super Coil cylinder

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    Default Fitting hot water kit thermostat to OSO Super Coil cylinder

    I'm about to start a major upgrade to our home heating, including fitting a new unvented tank and Evohome for heating, and ideally water.

    While I can see how to connect in the Evohome water kit via the relay, I'm struggling to find information on the suitability / ease of compatibility of different unvented cylinders with the Evohome cylinder temperature sensors.

    From what I can see from diagrams / comments Megaflo has a spare temperature pocket in the immersion assembly; Gledhill has a spare temperature pocket at the same elevation as the overheat thermostat; but the OSO doesn't seem to have any specific provision?

    Our preferred installer would like to fit OSO as that's what he is used to working with, so I wondered whether anyone had experience of integrating OSO and Evohome.

    Thanks in advance for any help!

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    Quote Originally Posted by StuartG View Post
    I'm about to start a major upgrade to our home heating, including fitting a new unvented tank and Evohome for heating, and ideally water.

    While I can see how to connect in the Evohome water kit via the relay, I'm struggling to find information on the suitability / ease of compatibility of different unvented cylinders with the Evohome cylinder temperature sensors.

    From what I can see from diagrams / comments Megaflo has a spare temperature pocket in the immersion assembly; Gledhill has a spare temperature pocket at the same elevation as the overheat thermostat; but the OSO doesn't seem to have any specific provision?

    Our preferred installer would like to fit OSO as that's what he is used to working with, so I wondered whether anyone had experience of integrating OSO and Evohome.

    Thanks in advance for any help!

    Some OSO cylinders have a clamp to hold the probe, on others OSO recommend that the probe is inserted against the metal cylindrical by forcing it through the foam insulation.
    If buying new you can specify the probe clamp.

    Give them a call for advice, I discussed with them at a recent trade show.
    I work for Resideo, posts are personal and my own views.

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    Spoken to OSO, and they were really helpful.

    What they said is that inside the control module the Ecoline cylinder has a clamp that can be used to fix the insertion sensor to the outside of the cylinder, while the Super S has a clip between the two facatory fitted thermostats that although not specifically designed for this can be used to fix the insertion sensor in place.

    So basically the insertion sensor is used as an external sensor, and no need to insert through / under the insulation.

    I'm happy to go with this, and hope the information above helps others.

    I'll try to remember to post back when the work is done to say how well it worked! I've learned a lot browsing this forum, and it's really made the decision for me to go ahead with Evohome, so looking forward to seeing it in action...

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    Quote Originally Posted by StuartG View Post
    Spoken to OSO, and they were really helpful.

    What they said is that inside the control module the Ecoline cylinder has a clamp that can be used to fix the insertion sensor to the outside of the cylinder, while the Super S has a clip between the two facatory fitted thermostats that although not specifically designed for this can be used to fix the insertion sensor in place.

    So basically the insertion sensor is used as an external sensor, and no need to insert through / under the insulation.

    I'm happy to go with this, and hope the information above helps others.

    I'll try to remember to post back when the work is done to say how well it worked! I've learned a lot browsing this forum, and it's really made the decision for me to go ahead with Evohome, so looking forward to seeing it in action...

    For the slightly older series 20 OSO tanks the only way of doing it was to jam the sensor inbetween the insulation and the inner metal tank. However, despite my concern with the reading accuracy of this, I found it measured spot-on. To validate this I left the original thermostat set to 60 degrees, and watched what temperature EVOHOME thought the water was when it cut out. It also read exactly 60 degrees. In your scenario you should have no problems at all. As was pointed out to me though, it is vitally important that you leave the OSO thermostat in series with the BDR91 A/B connections. In this way if EVOHOME fails and the water is left getting hotter and hotter, the OSO thermostat will cut out. The OSO thermostat actually itself contains 2 thermostats in series, the adjustable one and the fail-safe one. What I did was set the OSO thermostat to 70 which is hotter than I would ever set it, but means I have a double barrier. In actual fact, it would be very hard to turn the OSO tank into a bomb, because most boilers are set to around 65-70 degrees C which means of course the water cannot get any hotter than that anyway! But these fail-safes are mandatory for legal compliance. There are pictures on the web of what happens when an unvented cylinder explodes...rightly fitted they have enough protection in place with pressure and temperature limiting valves, but I know it's put a few people off in the past who are worried they have installed a bomb in their house.

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    Quote Originally Posted by jonstatt View Post
    For the slightly older series 20 OSO tanks the only way of doing it was to jam the sensor inbetween the insulation and the inner metal tank. However, despite my concern with the reading accuracy of this, I found it measured spot-on. To validate this I left the original thermostat set to 60 degrees, and watched what temperature EVOHOME thought the water was when it cut out. It also read exactly 60 degrees. In your scenario you should have no problems at all. As was pointed out to me though, it is vitally important that you leave the OSO thermostat in series with the BDR91 A/B connections. In this way if EVOHOME fails and the water is left getting hotter and hotter, the OSO thermostat will cut out. The OSO thermostat actually itself contains 2 thermostats in series, the adjustable one and the fail-safe one. What I did was set the OSO thermostat to 70 which is hotter than I would ever set it, but means I have a double barrier. In actual fact, it would be very hard to turn the OSO tank into a bomb, because most boilers are set to around 65-70 degrees C which means of course the water cannot get any hotter than that anyway! But these fail-safes are mandatory for legal compliance. There are pictures on the web of what happens when an unvented cylinder explodes...rightly fitted they have enough protection in place with pressure and temperature limiting valves, but I know it's put a few people off in the past who are worried they have installed a bomb in their house.
    My OSO 20RD has used the surface inserted probe without any issues for the past 9 months. The Top Limit safety cutout is factory set at 85 +/- 3C. The other warning that you should perhaps be giving is that the only people who can legally carry out work on unvented hot water systems - for the reasons that you give above - are engineers who have been trained to meet the requirements of the Building Regulations Approved Document G (section G3).


    http://www.citb.co.uk/documents/cski...nformation.pdf
    Last edited by HenGus; 4th April 2015 at 10:31 AM.

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    Thanks for the comments. Sounds likes this will work with the OSO. As I see it, the evohome relay effectively functions as the timer/programmer in a traditional set up / wiring arrangement. The cylinder's own thermostat and safety go in series, so the cylinder is installed exactly per manufacturer's instructions, and if any thermostat sees a temperature above its set point it cuts the circuit, closing the zone valve and stopping the boiler. The difference is the evohome calls for hot water to be heated, in place of a simple programmed schedule. I had assumed the regular cylinder thermostat (not the safety) would be set higher than evohome, so evohome has control.

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    My set up, as explained to me by the installer, is that Evohome HW kit is linked in series with the normal thermostat. You are correct that for the Evohome to work properly, the cylinder stat has to be set higher than the Evohome setting. There is also an immersion heater thermostat: on the 20RD, the temperatures are set independently. The Top Stat should over-ride both if the temperature rises to the Top Stat setting. With the Evohome HW kit, both Evohome and the normal cylinder stat would have to fail before the Top Stat kicks in.

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