Scalding water with Hive

daleb · 24 Jan 2026

I recently did a DIY instal of a multizone Hive system in our newbuild home. However, since the install was completed, the water out of each tap in the house is now scalding hot. Previously our water would come out at about 40°C when the tap was set to fully hot now thats just below 60°C.

The water is heated via a water tank (Megaflow Eco SystemReady Unvented Cylinder) and Baxi System15 boiler.

Electrically, everything looks to be in good order and HW valve is shutting off as expected when hot water is turned off via hive app.

There doesnt appear to be any sort of TMV blending valve at the flow end of the tank or next to any of the sinks.

Anyone have any suggestions as to what I could do to fix?

polesapart · 24 Jan 2026

daleb said:
Electrically, everything looks to be in good order and HW valve is shutting off as expected when hot water is turned off via hive app.

Then the cylinder stat is faulty or miswired, more likely the the latter. Or set too high.

dilalio · Sunday at 7:51 AM

What is the actual temperature at a tap?
What is the cylinder stat set to?
Is your immersion heater on?
Do you have a secondary return.

Need actual temps because scalding is different to individuals..

CountryFan · Sunday at 8:29 AM

40 degrees seems too low anyway for cylinder fed hot water.

daleb · Sunday at 9:45 AM

polesapart said:
Then the cylinder stat is faulty or miswired, more likely the the latter. Or set too high.

The cylinder worked fine before hive and there was no interference with the wires involved when installing the Hive system so it would have to have gone faulty as a coincidence at the exact same time. Temp adjustment didn't move either.

dilalio said:
What is the actual temperature at a tap?
What is the cylinder stat set to?
Is your immersion heater on?
Do you have a secondary return.

Need actual temps because scalding is different to individuals..

Temp at tap is as I said above 60°c.

Can't tell what the stat tempt is as the adjustment scre has no values and there is no gauge but it hasn't been adjusted or anything during the swap over.

Emersion heater is off.

Cant see a secondary return, just primary.

CountryFan said:
40 degrees seems too low anyway for cylinder fed hot water.

We did always think it was quite low but 60 is way too hot, especially with young kids in the house. That was tap temps.

dilalio · Sunday at 9:54 AM

daleb said:
The cylinder worked fine before hive and there was no interference with the wires involved when installing the Hive system so it would have to have gone faulty as a coincidence at the exact same time. Temp adjustment didn't move either.

Temp at tap is as I said above 60°c.

Can't tell what the stat tempt is as the adjustment scre has no values and there is no gauge but it hasn't been adjusted or anything during the swap over.

Emersion heater is off.

Cant see a secondary return, just primary.

We did always think it was quite low but 60 is way too hot, especially with young kids in the house. That was tap temps.

Are you measuring it with a thermometer or just guessing?

60°C is set on cylinders to prevent legionella but if water is constantly being drawn through and used up then risks are minimal and it can be lowered, but I would say 40 is too low.

Recommend blending valve(s) or thermostatic taps.

daleb · Sunday at 10:04 AM

dilalio said:
Are you measuring it with a thermometer or just guessing?

60°C is set on cylinders to prevent legionella but if water is constantly being drawn through and used up then risks are minimal and it can be lowered, but I would say 40 is too low.

Recommend blending valve(s) or thermostatic taps.

We have a water thermometer to measure the water tap out of the taps but I dont have anything I can check the cylinder temp with.

I beleive the cylinder is probably set at 60 based on the requirements for newbuilds. We didn't adjust the cyclider at all during install so cant see how this would have changed.

daleb · Sunday at 10:18 AM

Could it be more likely that there was something wrong with the way the old system was setup and now that it has been changed over its now working as it should? Reading online has tap temp as being between 50-60°C as standard which is where ours now currently falls.

dilalio · Sunday at 10:25 AM

daleb said:
Could it be more likely that there was something wrong with the way the old system was setup and now that it has been changed over its now working as it should? Reading online has tap temp as being between 50-60°C as standard which is where ours now currently falls.

Yep... As said... Stored hot water needs to prevent legionella.

Madrab · Sunday at 10:35 AM

daleb said:
Temp at tap is as I said above 60°c.

daleb said:
Previously our water would come out at about 40°C when the tap was set to fully hot now thats just below 60°C

If the cylinder stat is set to 60deg and the system temp is > 60deg then depending on the travel distance to the tap and the insulation of the HW pipework, then HW should reach 60deg in the cylinder and then arriving at the tap @ ~55deg, would be spot on. If there are no blending (TMV) valves (new builds should have them on baths etc) then the system is working as it should.

As mentioned, HW at the outlet @ 40deg, with no blending involved is really too low, specs suggest 50deg min, that would suggest that either the cylinder stat was set too low or the system temp was set low and the HW was never reaching 60deg.

ericmark · Sunday at 1:27 PM

Not a plumber, but I thought these

valves allow cooler hot water from the taps where mixer taps are not used, the tank water temperature is over 60°C, I used to set immersion lower to boiler, so boiler has priority, today the immersion is cheaper to run to boiler so don't do that any more.

Madrab · Sunday at 2:13 PM

ericmark said:
Not a plumber, but I thought these valves allow cooler hot water from the taps where mixer taps are not used, the tank water temperature is over 60°C .....

As per the 2010 revised regs - all new builds or new baths in existing should have TMV2 mixing valves fitted to baths, regardless of tap types.

dilalio · Sunday at 3:37 PM

dilalio said:
Recommend blending valve(s) or thermostatic taps.

ericmark said:
Not a plumber, but I thought these

valves

Harry Bloomfield · Sunday at 6:16 PM

daleb said:
We did always think it was quite low but 60 is way too hot, especially with young kids in the house. That was tap temps.

It needs to be stored, hot enough to kill any Legionella - that means at least 55C. To avoid scalding, then fit TMV's, to cool the water for use.

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Scalding water with Hive

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