EVOHOME with unvented water cylinders

[Apache_sim]

Hi
I would like to fit the EVOHome kit to my system, but I am finding it difficult to get a definitive response to fitting the wireless Cylinder Thermostat (CS92).
I have a Thermecon Dualstream 300 cylinder that is fitted with a CAEM cylinder Thermostat and also a CAEM High Limit Thermostat sharing a common immersion well. One installer says that he has never found an unvented tank he could not fit the CS92 to. When I asked about the fail safe addition of the High limit stat i felt he was bluffing, and would just remove the High stat leaving the CS92.

Is this a safe option?

Or does the CS92 cover both jobs (I cannot see that myself.

Thanks for any advice on fitting the CS92 to an unvented system

Mick

[johnwharrison]

I believe the rule of thumb is NEVER remove the overheat stat on an unvented cylinder.

You'll be on your way to turning it into a bomb

https://www.youtube.com/watch?v=9bU-I2ZiML0

[HenGus]

I have an Oso Unvented cylinder with no spare access ports. When I contacted Oso last year, their technical team were adamant that nothing should be done to the existing stats protecting the cylinder from an overheat situation. Their suggestion was that the Evohome HW kit should be wired in series with the existing cylinder stat. The probe is inserted, in my case, via the electrical access panel under the insulating foam but lying against the cylinder about a 1/3 up from the bottom. The existing cylinder stat is set a few degrees above the Evohome setting such that Evohome controls my HW temperature and boiler demand. If Evohome fails then the existing stat will take over. If that stat fails then the high limit safety stat should kick in. If your chosen plumber is not aware of these constraints then he is probably not Gas Safe qualified/certified to work on unvented hot water systems.

[Apache_sim]

I have an Oso Unvented cylinder with no spare access ports. When I contacted Oso last year, their technical team were adamant that nothing should be done to the existing stats protecting the cylinder from an overheat situation. Their suggestion was that the Evohome HW kit should be wired in series with the existing cylinder stat. The probe is inserted, in my case, via the electrical access panel under the insulating foam but lying against the cylinder about a 1/3 up from the bottom. The existing cylinder stat is set a few degrees above the Evohome setting such that Evohome controls my HW temperature and boiler demand. If Evohome fails then the existing stat will take over. If that stat fails then the high limit safety stat should kick in. If your chosen plumber is not aware of these constraints then he is probably not Gas Safe qualified/certified to work on unvented hot water systems.

It is my plumber that is querying the Honeywell Installation Instructions. It was an independent fitter that said it wouldn't be a problem. If I can fit the additional sensor into the immersion well, I like the idea of maintaining the original stats. The Cylinder I have does not offer access to the foam.
Thanks for the help
Regards
Mike

[Fursty Ferret]

I believe the rule of thumb is NEVER remove the overheat stat on an unvented cylinder.

You'll be on your way to turning it into a bomb

https://www.youtube.com/watch?v=9bU-I2ZiML0

You shouldn't interfere with the overheat stats on an unvented cylinder because of regulations, but it's not particularly dangerous. Think about it - your boiler will simply cycle on and off on it's own stat if it's left on; and if that fails you've got an overpressure relief on the cylinder. Even the manufacturers are blasé about it because they don't insist that the boiler demand is wired through the stat, so in the event that the microswitch on the valve fails in the closed position, or the valve sticks open, the hot water is permanently on. You do get an enormous gas bill, mind...

It's common sense to wire the hot water demand in series with the existing stat (wound up to the upper limit) in case the BDR91 goes haywire, but you're not going to blow up your house. Even if you did manage to get your tank to 100C or more, the risk is severe scalding when someone turns a tap on and the hot water instantly vaporises into a cloud of superheated steam.

There are many ways of safely fitting the Evohome thermostat to an unvented cylinder. I removed the existing probe for the immersion heater, electrically isolated it, and stuffed the Evohome probe down t'orifice.

[Fursty Ferret]

It is my plumber that is querying the Honeywell Installation Instructions. It was an independent fitter that said it wouldn't be a problem. If I can fit the additional sensor into the immersion well, I like the idea of maintaining the original stats. The Cylinder I have does not offer access to the foam.
Thanks for the help
Regards
Mike

Hi Mike,

If your plumber is trained to work with unvented cylinders he'll know that the existing stats must be maintained. However, he could drill a small hole in the steel casing, remove a bit of insulation, and then push the probe in so that it's trapped between the insulation and cylinder wall (use a bit of heat conductive paste too). He can then secure the cable and seal the hole with a decent squirt of silicone.

[Apache_sim]

Hi Mike,

If your plumber is trained to work with unvented cylinders he'll know that the existing stats must be maintained. However, he could drill a small hole in the steel casing, remove a bit of insulation, and then push the probe in so that it's trapped between the insulation and cylinder wall (use a bit of heat conductive paste too). He can then secure the cable and seal the hole with a decent squirt of silicone.

Thanks Fursty Ferret, that all makes sense.
i have requested support from Honeywell who have not responded. I think my plumber is also trying but without success too.

I can't believe that this is the first time this has come up with the Evo Home install..

Thanks for all the advice

[top brake]

Thanks Fursty Ferret, that all makes sense.
i have requested support from Honeywell who have not responded. I think my plumber is also trying but without success too.

I can't believe that this is the first time this has come up with the Evo Home install..

Thanks for all the advice

What is your exact question please? The evohome installation manual covers this. The youlearn training covers this. Sounds like your installer is not G3 approved? Maybe look for a Honeywell connected specialist that has experience. It is an everyday thing.