New to Evohome - Pump Speed with Opentherm

[mrrodge]

Hi, first post.

Last night I set up my R8810 and my Evohome thermostat with a load of HR92's.

All seems to work well, except my motivation for buying into Evohome was to get the most out of my shiny new Ideal Vogue Max 40, which previously had an ESI on/off stat with the CH flow temp set to 65C at the boiler.

Before installing Evohome I spent a few days getting the balancing as good as I could get it (I have a mix of old and new rads) and had a flow/return of 65/58C at the boiler plus a drop ranging from 1-8C at the rads (most were about 4C in the end, the 1/8 were the outliers that I couldn't get any better). Obviously I want to try and get the return temp lower than this for condensing.

I have a fairly big radiator in the hall with no TRV and the lockshields fully open to act as a bypass. Looking at the install manual for my boiler, this is easily big enough to satisfy the 10% of minimum output. I wanted to have this as a zone with the Evotouch showing the temperature in the hall but no joy - the zone disappears as soon as I add my first TRV to another zone. Is there a way to display the temp?

I noted that pump modulation was enabled on my boiler and I never saw it running any faster than 72% before installing Evohome. Since I installed last night though the pump seems to run at a fixed 85%. This, combined with only the rads calling for heat being on (as opposed to them all) appears to be causing a zero drop at the boiler (this morning was 57/57C). I can see the flow temp/burner is being modulated, which is a good thing (lowest flow temp I've seen so far has been 52C) but there's never any drop on return, suggesting the pump is too fast. Is there anything I can do about that?

Also I'm unable to register online for TCC - the form just throws an 'oops' error. Any ideas?

Thanks!

[Richard]

Ideal Heating boilers and pump speed...

From an engineering perspective, you would like to think heating systems vary in size and therefore one pump (speed) doesn't fit all, so the pump should be fully adjustable right? Well, yep this should 100% happen, but for whatever illogical reason Ideal Heating have chosen not to allow the installer/homeowner to change the pump adjustment. This makes balancing quite hard.

So for this situation, I would recommend IMI Automatic Flow Control Radiator Valves as the only solution (https://theintergasshop.co.uk/radiator- ... 61800.html). These correctly and accurately control flow rates through the radiator, irrespective of pump speed setting.

Also the only 'bypass' you want on a system, is an automatic one. Leaving a radiator fully open could be really reducing the efficiency of the boiler by allowing really hot water to pass back to the boiler and therefore taking it out of condensing mode.

A condensing boiler should be achieving a 20C temp drop across each radiator, when the room is at its design temperature (21C for instance).

[mrrodge]

Thanks for the quick reply - much appreciated.

I do believe I had it pretty well balanced regardless - the pump speed didn't seem to change until I installed Evohome.

When I did my Googling for balancing the system (nope, I'm not a plumber and no, the plumber who installed it wasn't clued up on any of this) I was under the impression that because I'm mixing rads that are 20+ years old with new ones, and the old ones weren't sized correctly, a 20C drop would be impossible for me, which has proven to be the case.

The issue I have is that Evohome seems to have decided to run the pump faster than it ran before (minimum speed is 70%, it's chosen or is locked by the boiler to 85% which I guess is 50% equivalent), which must have contributed to the return temp being too high. Or is that wrong? It also stands to reason that I'll lose some of the drop when the rad valves close as well, as there'll be nowhere to go for much of the hot water other than back to the boiler.

I'm not up on bypass valves - why do I need it/what does it do exactly? My boiler installation manual says the boiler has one but it still needs to use a radiator with at least 10% the heat output of the minimum boiler output, which is why I set my heating up this way.

TBH, the thought of spending another £300+ and countless hours changing valves makes my stomach churn, after I've already invested £1k in the Evohome kit knowing it will never pay for itself.

[Richard]

Thanks for the quick reply - much appreciated.

I do believe I had it pretty well balanced regardless - the pump speed didn't seem to change until I installed Evohome.

When I did my Googling for balancing the system (nope, I'm not a plumber and no, the plumber who installed it wasn't clued up on any of this) I was under the impression that because I'm mixing rads that are 20+ years old with new ones, and the old ones weren't sized correctly, a 20C drop would be impossible for me, which has proven to be the case.

The issue I have is that Evohome seems to have decided to run the pump faster than it ran before (minimum speed is 70%, it's chosen or is locked by the boiler to 85% which I guess is 50% equivalent), which must have contributed to the return temp being too high. Or is that wrong? It also stands to reason that I'll lose some of the drop when the rad valves close as well, as there'll be nowhere to go for much of the hot water other than back to the boiler.

I'm not up on bypass valves - why do I need it/what does it do exactly? My boiler installation manual says the boiler has one but it still needs to use a radiator with at least 10% the heat output of the minimum boiler output, which is why I set my heating up this way.

TBH, the thought of spending another £300+ and countless hours changing valves makes my stomach churn, after I've already invested £1k in the Evohome kit knowing it will never pay for itself.

OK, so lets first talk about Ideal Heating... They give really bad advice and I have concerns over the competency of their tech dept/boiler development team. The boilers they sell are not optimal for the bulk of homes in the UK.

As for your radiators, any radiator is capable of DT20 if you have the correct flow rate through it. Unfortunately, people don't realise how little flow you need for some radiators in a DT20 system. However, you need to see if the radiator is adequately sized for the room at say a 70/50 (or lower 60/40 or 50/30) design. Also every room should have the correct sized radiator in it, to give the correct output for the heat loss of that particular room at -3 deg C outside. Radiators shouldn't be any more than 5% under or oversized when comparing to the other rooms.

An 'open circuit' radiator, doesn't mean the radiator should have its lockshields wide open either. This radiator should be balanced to DT20, the same as all radiators on a condensing gas boiler system should be (if the designed flow temperature is over 50C). In my opinion, the days of open circuit radiators should not exist, and external Automatic Bypass Valves (https://theevohomeshop.co.uk/honeywell- ... valve.html) should be fitted and correctly set where minimum boiler flow rates are required. We should not be relying on a certain amount of open circuit radiators in lieu of this, as it can be really wasteful and does not promote optimal efficiency of a heating system with a condensing boiler fitted to it.

The issue you have is the pump speed is way too fast. Very hard to balance a system when the pump is giving you 6 meters head pressure and you only need 1 or 2. Maybe complain to Ideal Heating and see what happens?

As for the comment of evohome not paying for itself, there have been many systems over the years where it has. evohome when used correctly, reduces energy wastage by accurately controlling air temperatures and when used with an Opentherm Bridge, keeps the boiler in condensing mode as much as it can. It can also be used to increase comfort in a home, but this can be at the expense of energy saving.