Honeywell H/W tank thermostat

[Tony L]

Hi, I have a standard Honeywell thermo unit strapped to the side of the tank. It was playing up, good water temp for a few days, hot but you could wash hands under it, just.. to the 5th day where it would be hotter than a kettle, scalding temp.

I replaced the unit, took mins, now does the same thing. I have removed the stat, carefully sanded the copper to expose fresh copper (tank is 30 yrs) jiggled it and then popped it all back on. Seemed ok for a week, then back to being scalding. Everything else in the system works. Heating is as good as, etc.. just when the water is that hot a) it's scalding hot b) the aqualisa pump suffers from air in the system and or week impeller as the water flow goes down.

Fiddle with the dial, set it back to 40 and then it settles back to normal temp. I run the shower with no hose to clear the system, then back to normal .

Any ideas on this irregular issue?

Thanks

 

[Chuck]

Any ideas on this irregular issue?

What's your plan here? Keep fiddling with it until, one day, the water in the tank starts boiling and your house is destroyed or someone is seriously injured?

Judging from your description, your system is currently in a dangerous state. Please, switch the heater off until wiring is checked and/or the thermostat is replaced with one that is properly fitted and works correctly.

A remote possibility is that the thermostat has a legionella prevention feature, which raises the temperature to 80°C every few days. If this is what's happening there should be a tempering valve on the outlet of the cylinder to limit the temperature of the hot water by mixing it with the right amount of cold.

 

[Tony L]

Update - I should have added this - if I turn up the dial on the thermostat (which goes to 80') the unit kicks in at 70, so there is a stop point. And the boilers not on 24/7 heating the water (Honeywell L641A Cylinder Thermostat).

I agree with your thought, I think I'd be very worried if it was non stop heating the water. But ironically, at 70 it stops - turn the dial a mm more it kicks in again.

I might swap out the unit again. Recommended temp in the install guide is 60/65.. seems hot but there you go

 

[Riley]

I bet it’s not the thermostat if it’s gettibg that hot. Have you tested the old thermostat to see if it’s broken?you can at least test resistance if you’ve got a multimeter

 

[Tony L]

Just checked the water temp 61' and not calling to be heated, I reckon it could be the safety legionella protection.

 

[Chuck]

I might swap out the unit again. Recommended temp in the install guide is 60/65.. seems hot but there you go

60°C is a minimum recommended temperature for stored water to avoid legionella. I say 'a' rather than 'the' because opinions differ.

 

[Chuck]

Just checked the water temp 61' and not calling to be heated, I reckon it could be the safety legionella protection.

AFAIK, the L641A doesn't have a legionella prevention mode. It's just a dumb thermostat that needs to be in good thermal contact with the cylinder.

Perhaps the HW valve it controls is sticking?

 

[Riley]

That’d be my call two or three port valve sticking

 

[fronty]

That’d be my call two or three port valve sticking

Just what I was thinking. Have had similar problems in the past with scolding water due to faulty TPV.

 

[Tony L]

Damn, do you know what. I also replaced the three way valve, the silver controller piece, not the entire unit (copper pipes) it was making this clicking/rattle noise for ages, replaced it, went away. Noise is now back - same time as the temp fluctuations
HONEYWELL V4073A MID POSITION VALVE POWER HEAD ONLY

The whole lots about to get replaced soon as the plans and extension is being done next four months.

 

[fronty]

All these TPV heads are such a Rubbish design, the motors stall to keep the valve open, constantly consuming 3-4W of power, getting hot and eventually burning themselves out. There must be something better out there.

3W x 24hrs x 365 = 26KW a year, multiplied by, oh I dunno, 25 million houses, that's about 657GW just to power these damn things!!!

 

[Tony L]

Tend to agree. My neighbours a plumber, though he won't help me replace it - says it's simple enough for me to do. Hey ho. Should be just a case of turn it all off, drain everything down. Then pop it out and rewire it, re fill with inhibitor, all done .

 

[steadyon]

fronty:

1. There is at least one alternative to the spring return valve, called a motor on / motor off (MOMO) valve. However, the wiring is more complicated, the valves are slightly more complicated and in consequence may be less reliable. Also, for example with unvented cylinders, there is a requirement for the valves to fail in the closed position. This is easier to achieve with a spring than with a motor.
2. With regard to your calculation:
2a. Most of them are 6w rather than 3.
2b. The motor is only activated during the heating and / or hot water "on" times. So more like 10 hours / day than 24.
2c. They may use a lot of power in total, but this is wholly insignificant in the context of total power usage.
2d. They cost the average homeowner about 6op a year to run.

 

[Tony L]

I'm going to call Honeywell tomorrow, just to double check if it's a built in warning to keep it at 60. I was at the inlaws today and their water was just as hit. Only issue in finding is the aqualisa shower pump just doesn't work as well. I take the hose off and let it run, still doesn't seem to help. Can't believe they'd have impellers that would be affected .

What would labour be do you think to switch it out.

 

[Riley]

Won’t be the thermostat