Help with Evohome / Opentherm / Intergas

[HenGus]

Maybe my google skills are lacking but I can't find anything to collaborate - can anyone else confirm if this is urban myth or fact ?

If its fact, any ideas how I can monitor the temperature of my megaflo without hacking the external insulation about ?

I am sure Honeywell will be along in a minute; however, I am not sure that setting an OT boiler relay changes anything in a practical sense. The HW kit is still communicating with Evohome via a BDR. Presumably, when there is a HW demand, the CH demand is over-ridden and Evohome tells the boiler to set 90C (limited by the TMax set on the boiler). Clearly, the HR92s will continue to open/close as required but with the potential for overshoots.

As far as the HW sensor is concerned, the probe on my Oso unvented cylinder has been pushed up at an angle under the tank insulation with access via the electrical panel cover. It's worked fine for the past 3 1/2 years.

[Dan_Robinson]

I am sure Honeywell will be along in a minute; however, I am not sure that setting an OT boiler relay changes anything in a practical sense. The HW kit is still communicating with Evohome via a BDR. Presumably, when there is a HW demand, the CH demand is over-ridden and Evohome tells the boiler to set 90C (limited by the TMax set on the boiler). Clearly, the HR92s will continue to open/close as required but with the potential for overshoots.

As far as the HW sensor is concerned, the probe on my Oso unvented cylinder has been pushed up at an angle under the tank insulation with access via the electrical panel cover. It's worked fine for the past 3 1/2 years.

Not quite.

The CSA communicates cylinder temperature data. BDR is an actuator. As you say though, in hot water mode Evohome sends max demand to the boiler. But it is not specified as hot water, so the boiler doesn't know the difference unless, like with the Intergas and Atag (assuming Faketag is the same as the old Atag) the BDR is wired to the boiler directly and let the boiler control that valve.

That way the boiler logic ramps the burner to heat the cylinder quickly.

Otherwise you could be left with the burner sitting at low modulation whilst the boiler thinks how to heat the house more efficiently.

Not sure what Paul means by "monitor the temperature of" the megaflow. The way cylinders heat, discharge and stratify make monitoring the temperature rather fruitless. I have often wondered exactly how the differential setting really takes effect outside of normal temperature degradation - if at all. If you actually monitor a boiler and cylinder in operation during a bath fill and reheat you'll see that monitoring things is pretty pointless up until the final few minutes of the reheat phase.

Had a customer recently where their cylinder went over temperature by quite some way. They were convinced it was a fault with Evohome. In actuality it was a very tall cylinder, and the problem was as the cylinder is heated from the bottom and that is where the sensor is; the top can get close to the boiler running temperature - so 70/80 degrees. When the sensor at the bottom hits setpoint (say 55) it switches off and then over time that top layer disseminates down to the bottom raising the temperature. Really a cylinder that size should have a destrat pump or secondary return, but.....

One thing home owners need to understand is that there can be too much information and not enough understanding. This is where Evohome is both a blessing and a problem sometimes.

[DBMandrake]

Not sure what Paul means by "monitor the temperature of" the megaflow. The way cylinders heat, discharge and stratify make monitoring the temperature rather fruitless. I have often wondered exactly how the differential setting really takes effect outside of normal temperature degradation - if at all. If you actually monitor a boiler and cylinder in operation during a bath fill and reheat you'll see that monitoring things is pretty pointless up until the final few minutes of the reheat phase.

Not pointless, but the reading is only representative of outlet hot water temperature under a few very specific circumstances, and of course it depends how far up the cylinder it is measured.

There are two things that can cause the reading to drop - one is gradual loss of temperature when hot water isn't being used, (for example when it is scheduled off) which will cause a roughly even loss of temperature throughout the cylinder depending on how well it's insulated - in this circumstance the lower reading on the evohome is what you will actually get out of the cylinder.

When it is scheduled on again and starts to reheat, if the sensor is positioned correctly at the same height as the top of the heating coils/heat exchanger about 1/3rd of the way up the cylinder then as it reheats the reading will also be valid and representative of output hot water temperature (as long as concurrent hot water use isn't drawing in cold water) because the hot coils near the bottom of the cylinder will cause convection currents - hot water will travel up the core of the cylinder and slightly colder water will return down the outer wall of the cylinder past where the sensor is heating the wall of the cylinder.

For the duration of the reheat while convection is taking place and the temperature is rising the reading is a valid reading - if it wasn't you wouldn't be able to accurately control the temperature of the hot water as the system wouldn't know when to shut off...

The other time the reading will drop is when hot water is used and cold water is drawn in the bottom. As you run the hot water initially the reading wont change at all until the stratified cold water approaches the height of the sensor but once it does start to change the reading will drop pretty quickly as the cold water approaches and passes the sensor. When this happens the reading is NOT representative of the output temperature in any way shape or form. It can quickly drop down into the 30's while you're still getting 55 degrees out of the tap for quite a long time...

Because it doesn't drop for a while then drops very quickly I've found the differential setting makes very little difference to how much hot water you can draw before a reheat is triggered - almost no difference at all whether it's set to 5 degrees or the default 10. It's mainly affected by the size of the cylinder and how far up the sensor is - the higher it is the more water you can run before a reheat is triggered...

Because of this I have the differential set down to 5 degrees based on the minimum hot water temperature I want before a reheat without having to worry about it reheating "too soon" when drawing off hot water due to the smaller differential, as it really doesn't make any difference when the reason for the reading dropping is cold water being drawn in.

You also notice a big difference in reheat time based on what the reason for the 5 degree drop in temperature is - if its been left to sit without use and the whole cylinder has cooled by 5 degrees it might take 15 mins to reheat to the set temperature as the entire cylinder is convecting and has to be reheated. However if the reading dropped by 5 degrees because some cold was drawn in the bottom then only the cold stratified portion of the cylinder convects with a static hot water layer on the top that is not participating, so it reheats much quicker, say 5 minutes.

Had a customer recently where their cylinder went over temperature by quite some way. They were convinced it was a fault with Evohome. In actuality it was a very tall cylinder, and the problem was as the cylinder is heated from the bottom and that is where the sensor is; the top can get close to the boiler running temperature - so 70/80 degrees. When the sensor at the bottom hits setpoint (say 55) it switches off and then over time that top layer disseminates down to the bottom raising the temperature. Really a cylinder that size should have a destrat pump or secondary return, but.....

That sounds to me like the sensor might have been below the heating coils or right at the bottom of them... for whole cylinder convection to give an accurate reading the sensor needs to be about in line with the top of the heating coils. I notice that Honeywell install docs say "1/4 to 1/3rd of the way up the cylinder", which is just a rule of thumb really - I made mine 1/3rd and as it happens that is pretty much in line with the top of the heating coils based on the indirect ports on the side of the cylinder, and it works well. (granted it's a small cylinder)

If the sensor was at the bottom of the heating coils or even below them then the convection down the inside walls of the cylinder would not pass the sensor properly and you would get exactly the symptoms you describe, as it would read colder than the top of the cylinder. But with the sensor in line with the top of the heating coils/exchanger it should read accurately unless it was a really narrow and tall cylinder that can't convect effectively.

[Dan_Robinson]

Damn this forum is a git for selective quoting (from a tablet in the bath).

From my direct measurements, I've found the top of the cylinder to be pretty stable once that initial hot slug is filtered down.

The cylinder I mentioned over heating had the sensor in both the original cylinder stat pocket then in the little extra one Heatrea provide. Exactly where that is in relation to the coil I don't know without looking at the books.

I agree with you about the differential setting however.

My cylinder is a small 170 litre Joule which is perfectly sized for our family of 3 with excessive hot water usage (SWMBO used it all cleaning today). It is set to stay hot all evening and give a 30 minute boost in the morning to keep her ocd cleaning happy.

The theory being, the boiler is measuring the cylinder with its of an sensor and controlling the burn directly based on the data it gets. Evohome just gives it a "go" signal.

[mylesm]

As someone who is considering an Intergas Boiler when will we know if the percieved problem is solved once and for all ie Richard do you have a timeframe for when you expect your fix to be "officially confirmed"
Thanks Mylesm

As the OP asked about Intergas and OT is there any update on the intergas OT percieved issues as I am holding off getting intergas boiler until The fix is confirmed and made public
thanks mylesm

[The EVOHOME Shop]

As the OP asked about Intergas and OT is there any update on the intergas OT percieved issues as I am holding off getting intergas boiler until The fix is confirmed and made public
thanks mylesm

The issues I have encountered are not Intergas related and in my opinion the Intergas boiler is not at fault, as it has worked perfectly well with other OpenTherm controllers.

[blowlamp]

The issues I have encountered are not Intergas related and in my opinion the Intergas boiler is not at fault, as it has worked perfectly well with other OpenTherm controllers.

The fact that Evohome was reported to function OK when used as a single zone with the Intergas and only having issues when in multi-zone mode, certainly pointed towards Evohome being the likely culprit.

[mylesm]

The issues I have encountered are not Intergas related and in my opinion the Intergas boiler is not at fault, as it has worked perfectly well with other OpenTherm controllers.

Thats Good To know but your other statements seem to imply there were certain issues

"
OK, lets be clear... On my initial assessment there seems to be an evohome 'setup' issue with the OpenTherm Bridge and hence why I have said 'installer error'... However, it only seems to manifest as an 'issue' with certain boilers such as Intergas (if I do exactly the same setup with Ideal Logic+ for example the issue doesn't seem to occur). So there is still a bit to do to get to the bottom of this, however the method I now use to set the equipment up means the 'issue' doesn't occur"

I am holding off purchasing an Intergas Boiler until this is clear And hopefully Richard can elaborate on his findings or how to overcome the percieved issues

thanks
mylesm

[mylesm]

Any futher update on this please
mylesm

[Dan_Robinson]

Further clarification will take some time. This is to give consistent, warranty backed information to the end users.

[Dan_Robinson]

Capture1.jpg

Low modulation.jpg

High modulation.jpg

Just to prove there is more than one boiler working properly.

For the record - Richard's is HR92's (not sure if he has hot water connected).

Mine is HCC80 and HM80 based UFH zones with a solitary HR92 zone (just for schits and giggles) with Hot Water Priority on a D Plan.

I'm having trouble with my office PC so those 3 pictures above were one hell of a mission to post up.

[Dan_Robinson]

Ignore the DHW temperature readings BTW.... Not sure where they're coming from yet - could be the boiler's hot water outlet sensor on the combination side. I'#m too busy at the moment to get the temp probes out to cross reference.

[mylesm]

Thanks For That Dan
I have all HR92 valves with an OV Boiler at the moment WB24RI works well but boiler is getting on a bit so trying to prevent future problems by changing out now
I really dont care what the issue was with intergas and OT as long as its resolved

[mylesm]

Ok I am almost ready to get intergas Boiler IT will be installed in an Open Vent System no Hot water Cylinder heating only all Rads have HR92 Valves with one Towel Rail left open to act as Bypass I am hoping to use opentherm anything I need to know or watch out for in setting it up
thanks mylesm

[bruce_miranda]

Now we're talking....lets see how this works out.