Evohome and boiler issues

[robj20]

Been having an issue with my boiler turning the burner off because it senses an error on the flow/return temp sensor.
Had ideal round to check it out, no faults found they changed the sensor anyway and left me a spare and monitored the system for a while and noted that occasionally the boiler would read the return temp higher than the flow, he suggested opening the auto-bypass another 1 or 2 settings and see how it gets on.

But on thinking about when it seems to do this, im wondering if its when evohome has so little demand for example one radiator on the lowest setting, the auto-bypass is flowing the majority of the water and as this circuit is so short and no where for any heat to go this causes the issue. Anyway to test this?

Does anyone else experience anything like this?

[DBMandrake]

We can't see the image. You seem to be trying to direct link an image from google drive ? You can't do that, at least not without third party workarounds like this.

As for your specific problem, all I can suggest is that there are specific, normal, corner situations where the return temperature may be higher than the flow temperature for a few seconds, and if your boiler is that picky about that being a "problem" (when clearly it isn't a real problem - where is the mystery heat going to come from except back from being stored in the radiators ?) then I'd suggest that's a design flaw of the boiler.

Some of these modern boilers try to be fair too clever and paranoid in sensing "faults" from what I've seen... (such as delta T errors) and seem ill equipped to deal with what can happen with smart, scheduled TRV's! (When for example they might all be scheduled to open at the same moment, which a house full of manual TRV's will never do)

[robj20]

The one reference I can find in the manual is about maintaining a 10% load via a bypass.

So I think in the future when I do my bathroom I will have that radiator on dual lock shields, and have a thermostat in there to call for heat, will evohome allow this with no zone valve in there.

Or I could move the bypass further away from the boiler so it can lose more heat.

[DBMandrake]

I don't see how moving the bypass further away will help with a situation where the return temperature is higher than the flow temperature, if anything it would make it worse ?

[robj20]

How so. The idea being with the increase in pipework via the bypass circuit it should lose more heat. Currently when water goes via the bypass it travels around 2 meters back to the boiler I could extend this to about 8 meters by moving the bypass to the landing.

[robj20]

I wish Evohome had some extra settings all it would take is some way to limit a valve so it doesn't close as much so I can maintain a minimum flow through a radiator. I could then set my hall radiator to always be on 10% or so.

[fezster]

Just open your bypass more to allow sufficient water to flow and / or add a radiator without a TRV to your system (assuming your zone valve does not shut the CH circuit down, in which case the bypass is mandatory). My gut feeling is the boiler is mistakenly reporting a higher return temperature because it's not able to move the heat away fast enough when your CH circuits have closed down.

[robj20]

Which way on an auto bypass valve do you turn to allow more flow through it, it's on about 0.3 bar at the minute do I go to 0.4 or 0.2?

I don't actually think it will fix the issue as the bypass path just can't lose enough heat to satisfy the boiler.

I might play with the stroke settings on one of my rads see if I can set it to not fully close.

Fezster each radiator on my system is a zone, that's the issue when they all close the heat has no where to go, and the bypass doesn't get rid of any heat so the boiler throws a fit when it senses the same or higher return temp.

[fezster]

From memory, it should be anti-clockwise and the number should reduce (i.e. 0.2 in this case). If you feel on either side of the bypass, you should be able to tell if it is passing water. The bypass on minimum setting (i.e. 0.1) should be able to pass a very large quantity of water.

[robj20]

Thanks for all the help.
My plan for tonight is to remove the HR92 from the hallway radiator and set it nice and low so that can be my bypass radiator, its central so heats both upstairs and down.
With the bypass when i get round to lifting the floor boards to get access im going to fully close it, have one radiator on and set it so it just starts to flow, that should limit how much hot water goes straight back into the boiler but also give a path when the system shuts down.

I have had an idea for the future about piping it so the bypass circuit includes the hall radiator, not sure how yet though, suppose i would need to remove the TRV valve, fit a lockshield then a T piece with a TRV valve and HR92 on one and the bypass valve on the other.
That way the hall would still be able to call for heat and control the heat to some degree but when only 1 or none call for heat the bypass would kick in and start flowing through the radiator.