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Tim Cooke
Tim Cooke,
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Experience:  Owner at Self-employed
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I have a Greenstar 30RI compact regular boiler with seperate

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I have a Greenstar 30RI compact regular boiler with seperate heating and hot water tank supplies. Due to the cold weather the hot water is switched on automatically and is now on most of the time. The hot water is very hot, almost boiling. Is there anything I can do to lower the temperature of the water and maybe stop the boiler operating for such long periods. Regards Tom
Assistant: Did you double-check the thermostat's settings? And what about the filters?
Customer: I have Hive controls and there is no fascility for adjusting the hot water temp.
Assistant: Do you plan on doing the work yourself?
Customer: Yes
Assistant: Anything else we should know to help you best?
Customer: Is there an internal thermostat in the boiler which controls switching on the boiler.
Hello TomHigh DHW temperature isn’t caused by the boiler. It’s either a faulty (or wrongly set) cylinder thermostat, or a failed/sticking motorised valve.Do you have motorised valves next to the cylinder?
Customer: replied 7 months ago.
No. There is a thermostat fastened to the side of the tank to sense the temp. The boiler manual says the hot water circuit will switch on at 7 deg and begin to heat at5 deg.

When you mention the boiler manual, are you talking about the frost protection?

Customer: replied 7 months ago.

OK. I think we can ignore the DHW frost protection for now, unless your boiler or cylinder is outside the house.

Has anyone worked on the installation recently, who might have adjusted the cylinder thermostat?

Are you able to see the thermostat and any scale next to its setting knob?

Customer: replied 7 months ago.
The boiler is new it was installed 3 weeks ago. It is fitted in an unheated garage. The thermostat on the boiler was part of the old boiler system, I don’t know if it is part of the new system. It can be adjusted.

I'm slightly unnerved by your last post - are you saying that an old part was fitted to the new boiler? I suspect you aren't, in which case are you saying that the old room thermostat was used? Or if neither of those, what old part was fitted and to what?

Customer: replied 7 months ago.
No,I mean the tank thermostat is part of the old system but I don’t know if it is used on the new boiler. As part of the new hive control there is a separate control unit which includes the room thermostat. Ivan also control the system from my mobile phone. The main problem is not the central heating but the hot tank water which I can’t control.

If the cylinder thermostat isn't being used then it's an act of incompetence on the part of the installing/maintaining engineer. Lets go with the idea that it's connected, but might be faulty. Can you either describe it, or post a photo of it?

Customer: replied 7 months ago.
The tank thermostat is just a small 2”x2” which is in contact with the copper tank and held in place by a curtain type spring which is wrapped around the tank, an electrical lead goes down to the boiler. I don’t think this is the problem since it is always warm at the tank and since the boiler is out in the cold presumably the internal thermostat switches on the hot water tank circuit automatically in cold weather. I’m going to bed now can we continue in the morning or not, if not thank you for your assistance. Tom

Yes - we can continue in the morning.

Please dispel all assumptions about what's working and what isn't. The only way to find the problem is to assume nothing and to test and diagnose. The water temperature is supposed to be controlled by the cylinder thermostat, so that's a prime suspect. It would be helpful if you can tell me what it's currently set to, without changing it, or post a photo of it.

Tim Cooke and other HVAC Specialists are ready to help you
Customer: replied 7 months ago.
I can’t continue with this discussion now. Thanks for all your help.I will be cancelling my membership now.Regards Tom