Boiler firing constantly for hot watere

[Johntheo5]

That probe should be located above the heating coil outlet, maybe a 1/4 to 1/3rd the way up between the coil inlet & outlet, can you post a photo sometime showing the layout.

I meant to ask you before this, can you programme the HW to stay off at night until say 0400 or 0500 in the morning, there will then only be one or two boiler fire ups?.

 

[pwater]

Yea, so the pipe on the left is the boiler hot flow, the pipe on the right is the cold inlet, and the grey box has the temp probe/thermostat etc.

As you can see it’s not very far up…excuse my rough and ready insulation

I have also bought a wee switchbot to turn off the HW cylinder during the night on a schedule, which somewhat negates the major issue of the constant fire ups, but I am very interested to understand why its happening in the first place, if I do have a leak, would rather sort it.

 

[Johntheo5]

Surprise surprise, no call back but a very experienced contributor on another site says ~ 15C switching for the Cotherm. I have a old Thermowatt T 105 RTS 2 stat here and I have to move it over "5 minutes" to make it switch On/Off, also see info on the Thermowatt Stat re "functional temperature hysteresis" where it gives a number of 8C +/- 4C which I take it to mean that it will switch between 4C and 12C which IMO is normal.
I wouldn't though just purchase another Cotherm GTLH3161 without confirming that it has similar switching characteristics as the Thermowatt(s).

TB / TBR | Thermostats | Thermowatt EN

TB / TBR: capillary single-pole thermostat without safety cut-out. Read more details and ask for information.

www.thermowatt.com

 

[pwater]

Surprise surprise, no call back but a very experienced contributor on another site says ~ 15C switching for the Cotherm. I have a old Thermowatt T 105 RTS 2 stat here and I have to move it over "5 minutes" to make it switch On/Off, also see info on the Thermowatt Stat re "functional temperature hysteresis" where it gives a number of 8C +/- 4C which I take it to mean that it will switch between 4C and 12C which IMO is normal.
I wouldn't though just purchase another Cotherm GTLH3161 without confirming that it has similar switching characteristics as the Thermowatt(s).

TB / TBR | Thermostats | Thermowatt EN

TB / TBR: capillary single-pole thermostat without safety cut-out. Read more details and ask for information.

www.thermowatt.com

Ok, so I am definitely not seeing that given the heat loss I am seeing on the unit, so would suggest that issue 1 is the thermostat is up the left or has lost the ability to switch using the differential. Thankyou!

Secondly, I isolated the hot water circuit, and am seeing the same heat loss as when I have it on, around 0.8 degree an hour. Just to clarify my numbers, as I think i was likely a bit more vague before:

With the hot flow on, I went from 58.5 degrees to 54.5 degrees in 5 hours
With the hot flow off, I went from 61.5 degrees (i have moved the thermostat a wee bit since) to 57.5 in 5 hours

The outside of parts of the tank are around 26 degrees when I check, other parts are 20/21 which is the ambient air temp. So to be honest, I am thinking something has damaged the insulation over time or when it was initially installed in parts, as I can't see any other reason for that kind of drop to be honest. I spoke to baxi (who now own santon) who basically said its more than we would expect, but its old, maybe time for a refresh...

Maybe just time for a new cylinder....?

Thanks

Paul

 

[Johntheo5]

You are measuring that 0.8C/hr close to the cold water inlet so it may not be representative of the actual cylinder loss which may well be less so I wouldn't just dash off and buy a new cylinder, I would get that stat replaced after ensuring that the switching differential is as shown for the Thermowatt(s), as you pointed out, you will then be reducing your losses to the primary water as the boiler should now only fire once instead of around 6/night, 20M of 22MM piping contains ~ 6L of water, + say 2L in the boiler HEX, heat 8L from 25C to 65cCrequires ~ 0.42kwh gas consumption so 2.1kwh saved for 5 boiler firings.

A loss of (if) 0.8C/hr is 0.8*24, 19.2C/24hrs or 300*0.8/860, 0.28kwh/hr = 6.72kwh/24hrs, also = a cylinder loss rating of 280 watts.

 

[pwater]

You are measuring that 0.8C/hr close to the cold water inlet so it may not be representative of the actual cylinder loss which may well be less so I wouldn't just dash off and buy a new cylinder, I would get that stat replaced after ensuring that the switching differential is as shown for the Thermowatt(s), as you pointed out, you will then be reducing your losses to the primary water as the boiler should now only fire once instead of around 6/night, 20M of 22MM piping contains ~ 6L of water, + say 2L in the boiler HEX, heat 8L from 25C to 65cCrequires ~ 0.42kwh gas consumption so 2.1kwh saved for 5 boiler firings.

A loss of (if) 0.8C/hr is 0.8*24, 19.2C/24hrs or 300*0.8/860, 0.28kwh/hr = 6.72kwh/24hrs, also = a cylinder loss rating of 280 watts.

Yep, fair point, it seems like a strange placement to be honest...

I will get a new thermostat, see where I stand and take it from there, thanks again for all your advice and help!

 

[pwater]

So I spoke to someone helpful at baxi earlier and they confirmed all their tanks are set to call for heat with even a 1degree drop….and that I should fit a timer.

I think there is an issue with the tank losing heat, but given it’s not insane, and I have it under control with a timer that’s prob my best option for now until I look at a replacement tank.

Not sure if anyone has any recommendations for a 300l unvented that has a differential…

 

[Johntheo5]

So I spoke to someone helpful at baxi earlier and they confirmed all their tanks are set to call for heat with even a 1degree drop….and that I should fit a timer.

This is simply unbelievable IMO.

So NO, you should fit a cylinder stat with a sensible switching differential like the three or four that I have installed/replaced on relatives vented cylinders.

I think there is an issue with the tank losing heat, but given it’s not insane, and I have it under control with a timer that’s prob my best option for now until I look at a replacement tank.

Not sure if anyone has any recommendations for a 300l unvented that has a differential…

 

[pwater]

This is simply unbelievable IMO.

So NO, you should fit a cylinder stat with a sensible switching differential like the three or four that I have installed/replaced on relatives vented cylinders.

It does seem strange, as it means every 'baxi' cylinder is calling for heat more often than needed, i.e every time someone runs a tap to wash their hands...appreciate I may be affected more as I do think the tank itself is maybe feeling its age, but seems odd.

I just am not sure if I can replace the thermostat with another one not meant for the unit, im sure it will raise all kinds of servicing/safety questions if something goes wrong..?

 

[Johntheo5]

Try and find out from Cotherm what the actual switching differential is for your model.

 

[pwater]

So cotherm have confirmed it’s basically 1 degree in that unit. Usually it’s 8-5 they said.

So seems it’s just the thermostat causing this issue!

 

[Johntheo5]

Between 8C & 5C is fine but a bit confusing when "cotherm have confirmed it’s basically 1 degree in that unit" do they mean that model GTLH 3161 has a switching differential of 1C or that its just faulty?
I emailed them a hour ago but a supplier said by eMail ( a few minutes ago) that

"it should say on the side, + OR - 5 degrees. But Technical has said its usually set at around 5.
Then of course it will come on depending on what its et at and how close it gets. So, let’s say 60 when it gets to about 55 it would kick in."

 

[pwater]

Hi

So unfortunately seems I had the wrong part number, as that was listed as a replacement for my tank, but the item in it is a BTS60109, the MD of cotherm confirmed this morning

'These are quite sensitive and have a tight tolerance (differential) which is designated by the system manufacturer.'

I then followed up and he said its very low:

'I would have to check the drawing to be sure on the exact differential, but this is a very accurate thermostat.'

So unfortunately seems im out of luck on that front! He said most other cotherm stats are between 5-8 degrees, but not this one.

Thanks for all your advice

Paul

 

[Johntheo5]

Its getting more confusing by the minute, the Coltherm BTS60109 is a twin capillary 3 phase stat?, is this the stat thats presently in your cylinder?? or what??

 

[pwater]

Ye

It’s getting more confusing by the minute, the Coltherm BTS60109 is a twin capillary 3 phase stat?, is this the stat thats presently in your cylinder?? or what??

Yes, that’s what’s in it, I made a mistake on the model before.