Honeywell tanks stat calibration

[reb78]

Has anyone else had issues with Honeywell tank stat calibration being out?

Specifically these - https://www.screwfix.com/p/honeywell-home-l641a-cylinder-stat/40051

We have three on our newly installed thermal store to control various pumps and the boiler and none seem to correspond with the expected readings across the tank. I.e. the lower one controlling the boiler is about 4inches lower than one comtrolling a pump circulating the central heating. The lower one clicks at about 55C when the one 4 inches higher clicks at 50C. No way should it be hotter lower down.

Are there more reliable brands? I thought Honeywell made decent stuff but they just dont seem right.

 

[Kayos]

They are all terrible

 

[reb78]

They are all terrible

Thats unfortunate. Have i got the best of a bad lot?

I tried my little thermal imaging device to see what the tank temp was at the points the stats are mounted so at least they could be set to the temps i want (even if thats not what they say) but it won't read the copper.

 

[Kayos]

I'm surprised the pump is on its own stat as well

 

[dobbslc]

Try a piece of black insulation tape on the copper.
You'll get a better reading, it might not be the actual temp but it should give you the differential between the levels.

 

[reb78]

I'm surprised the pump is on its own stat as well

With the rayburn connected we wanted to be able to circulate heat all day independent of the oil boiler. So the stat to that pump is just beneath the CH flow and we want to switch that pump on when that level reaches 55C

The oil boiler has a seperate pump on the flow and is controlled using the room stat/timer/another tank stat and will come on if needed and the CH flow pump will operate as above when that bit if the store gets to 55C.

There is a third pump and stat at the top of the store - we want that to come on if the rayburn is getting the top too hot and it simply circulated the rayburn flow to the bottom of the tank. Without that the rayburn is just working on gravity the rest of the time so couldnget the top of the store too hot.

I probably havent explained it well but the setup makes a lot of sense for what we want. But thats why we need these stats to do their thing at appropriate temps.

In summer when we just want hot water we simply turn the CH flow pump stat up so it never comes on.

The Rayburn complicated a normal install i think. We have additional ports for solar and a log burner back boiler. Plus an immersion fitted if needed.

 

[reb78]

Try a piece of black insulation tape on the copper.
You'll get a better reading, it might not be the actual temp but it should give you the differential between the levels.

Thanks! Will do. The thermal imaging camera wont boot now but thats for tomorrow!

 

[reb78]

If anyone does know of a decent tank stat I would be happy to hear what make etc! They cant be that hard to get right with todays technology!

 

[Ross365]

The bi-metallic temperature switches are very often poor; it's really old technology, surprised its still around. honeywell used to make good stuff; I've got a good Honeywell programmed stat I bought in 1986 which still works but the one I bought 10 years ago lasted no time.

 

[dobbslc]

Not cheap and I'm not sure it'll do what you need but maybe a digital stat would be more accurate.

EPH RFC Wireless Cylinder Thermostat - With Receiver (RFCP) - Heating Controls Online

Control your hot water precisely with the EPH RFC Cylinder Thermostat from Heating Controls Online. Ensure efficient heating & save energy. Shop now!

www.heatingcontrolsonline.co.uk

 

[reb78]

Not cheap and I'm not sure it'll do what you need but maybe a digital stat would be more accurate.

EPH RFC Wireless Cylinder Thermostat - With Receiver (RFCP) - Heating Controls Online

Control your hot water precisely with the EPH RFC Cylinder Thermostat from Heating Controls Online. Ensure efficient heating & save energy. Shop now!

www.heatingcontrolsonline.co.uk

Wow! They are some money! It doesnt say but I wonder what how they get their reading from the tank?

 

[dobbslc]

Some I looked at need pockets but I'm not sure about that one.

 

[mike os]

Cylinder stats are as accurate as they need to be for their intended purpose…
For greater accuracy you would probably need bulb thermostats , pt100 or thermocouple in thermowells.

Or stick on pt100 direct to the tank.

Personally I would ignore the reading on the device and just make it work

 

[reb78]

Cylinder stats are as accurate as they need to be for their intended purpose…
For greater accuracy you would probably need bulb thermostats , pt100 or thermocouple in thermowells.

Or stick on pt100 direct to the tank.

Personally I would ignore the reading on the device and just make it work

I can do that if I can read the temps so I can make them switch on and off at the temps i want them to. The thermal imaging camera is working now so will put some black tape on specific spots tomorrow and see what it reads vs the stat.

 

[reb78]

Some I looked at need pockets but I'm not sure about that one.

I saw a few like that too. What surprises me is that there aren't some with sensors that touch the tank and use a thermal paste etc.

 

[knighty]

I'd just fit some of these... https://www.ebay.co.uk/itm/314010344508

wire into the cooling connection so when tank goes over X temp the pump/whatever ticks on

I don't really trust the 10amp rating of them.... but your pumps will only be about 1amp anyway?

although they're cheap I've used and abused loads, some hot/cold/wet etc. and they're all really reliable
(obviously your mileage may vary)

put a bit of thermal paste (or coper slip) on the temp probe and put them in behind your old tank stats to hold them to the tank

hardly use any power and you'll get a nice temp readout so you know what the tank is doing


you can set the temp difference between switch on/off too..... so if you want it on at 55'C and off at 50'C set it to 55'C with a 5'C temp difference

 

[Ross365]

I'd just fit some of these... https://www.ebay.co.uk/itm/314010344508
I don't really trust the 10amp rating of them.... but your pumps will only be about 1amp anyway?

They do look good, but the price is a bit low. It says the sensor is NTC which I think implies that the device is a thermistor, so that's good. Downrating the 10amp spec might well be good idea. Tempted to buy one just have on the shelf. I see that the voltage rating is 110-220V. I'm usually up around 246V here.

With all cheap stuff from the far east, there is little quality control, so one item comes down the product line and is perfectly good but the next one following it could be perfectly rubbish - a bit of a lucky dip sometimes. the cheapo battery charger I bought last summer lasted 3 months and then boiled a battery when it failed to shut off .

 

[Gareth J]

I've used horstman htc2 a few times. I'm not sure they are accurate, but they do seem to be consistent. Although rated for 16A, they don't like high amps through them; the current warms the unit, which is of course burried in insulation, which prematurely opens/closes the contacts.

Any pockets available? They might be more accurate.

You could put your Rayburn overheat thermostat at the bottom of the tank, next to the return to the Rayburn. The Rayburn overheating the water is only going to be an issue if its return gets too hot. Or a pipe thermostat on either the flow or return to the Rayburn. I would have the overheat stat fire the radiator circuit but wired to bypass the room stat. If your Rayburn starts to flow water that's getting too hot, you want to feed it cooler water. By turning on the rads circuit, you quickly cool the lower portion of the store with radiator return water and therefore have a supply of cooler water to quench the Rayburn. What happens in your setup in a scenario where the Rayburn could eventually get the entire store overheated? Also, power cuts?

 

[reb78]

I've used horstman htc2 a few times. I'm not sure they are accurate, but they do seem to be consistent. Although rated for 16A, they don't like high amps through them; the current warms the unit, which is of course burried in insulation, which prematurely opens/closes the contacts.

Any pockets available? They might be more accurate.

You could put your Rayburn overheat thermostat at the bottom of the tank, next to the return to the Rayburn. The Rayburn overheating the water is only going to be an issue if its return gets too hot. Or a pipe thermostat on either the flow or return to the Rayburn. I would have the overheat stat fire the radiator circuit but wired to bypass the room stat. If your Rayburn starts to flow water that's getting too hot, you want to feed it cooler water. By turning on the rads circuit, you quickly cool the lower portion of the store with radiator return water and therefore have a supply of cooler water to quench the Rayburn. What happens in your setup in a scenario where the Rayburn could eventually get the entire store overheated? Also, power cuts?

My understanding is that the stat on the Rayburn is more of an underheat stat? I.e. it should cut the power to the CH pump if the temps fall below 50C? Not sure if it can be wired in an alternative way though?

What we have done is put a stat on the tank just under the CH flow pipe and set that at 55C, when the stat reaches 55, it triggers the CH pump. So this is independent of the boiler central heating controls to an extent - realistically the Rayburn is never going to get the house too hot (its 50,000 BTU at full chat and the boiler for the house is specced at double that). So this way, heat from the Rayburn is always circulated and keeps the house a nice ambient temp (around 19C it seems from having had it on about a month now). This way the tank will never overheat as the heat is dumped when the lower third of the tank reaches 55C.

The boiler is controlled by the timer/room/tank stat more conventionally except that the CH circulation is still as above - so the CH will circulate when the stat controlling that pump reaches 55C. If the room stat isnt satisfied, the boiler will keep firing and the CH will keep circulating. We have hardly had the boiler on since the Rayburn was lit a month ago (maybe for about four hours in total)

Hopefully that makes sense.

In a power cut we would need to reign the Rayburn back, switch it so the heat goes to the oven and kitchen and less to the boiler and then have a bath if things get too hot . We contemplated a leak rad on the system and can add one later if needed but decided not to and to get the heat into the store and around the house instead. Its not much of a risk when we are out as its always left topped up and damped down on tickover as no point having it racing if we are out so nothing will get too hot then. Eventually i want a generator setup to run the boiler and pumps in a powercut. I know where the supply for the lot is so this would be fairly easy to rig up.

 

[brightspark]

I can do that if I can read the temps so I can make them switch on and off at the temps i want them to. The thermal imaging camera is working now so will put some black tape on specific spots tomorrow and see what it reads vs the stat.

you can get strap on temperature gauges that go on pipes easy enough and cheap bruv has one on his rayburn cooker https://www.ebay.co.uk/itm/20354528...=5338365712&toolid=20006&customid=EB88319644&