Intergas combi hot water temperature

[Johntheo5]

Your calcs, above, are quite correct.

There are a few questions re the rated output of this boiler, the MIs that I looked at shows a gas rate of 3.46m3/hr ~ 38.06kW, IF the boiler is 36kw output then its efficiency is 36/38.06, 94.6% (a bit on the high side), if the output is 32.7kW then the efficiency is 32.7/38.06, 85.9% ( way too low expectation for a condensing boiler.
Then it states that the "36" will give a DHW flowrate of 14.5LPM at a dT of 35C which means a heat input/boiler output of 14.5*60*35/860, 35.4kW (close to a "36kW boiler), it also states that the lower value input (MIs & post #2) is 32.7kW, equals and if true then the DHW output is only 13.39LPM at a dT of 35C.
Your installation data shows a (measured? gas rate of 3.34m3/hr which is "only" 3.34/3.46, 96.53% of its design gas rate, so ~ 36.74kWh or a boiler output of 36.74*0.88, 32.33kW so one way or the other, if you want the maximum possible boiler output you need to get somebody to check/recalibrate the gas rate (as suggested above), if not then just accept that its max output is, just about 29.0kW.

The reason Mira specify a minimum DHW temp of 55C is probably because the mixed max shower output is ~ 45C and 10C is a recommended dT between the HW and the , mixed flow outlet emperature, this shouldn't, IMO, cause the problem you have, but what you can do while awaiting your spares is to set the DHW temp to 65C and then (assuming a max boiler output of 28kW) control the max shower flow to 11.47LPM or less which means a mixture of 7.31LPM at 65C + 4.16LPM at 10C to give 11.47LPM at 45C.

 

[tfspark]

I’m assuming the 3.34 m3h is measured as it was written in the manual by the installing engineer.

I have just checked parameter P70 in the boiler. Max dhw output %. It was set to 95. I have set it to 100. Only slight increase but worth a try. I have not yet remeasured the temps.

In the meantime I’ll set the shower flow rate to 10 lpm and see what happens. I think when it was a permanent fault in January it didn’t matter what you did to flow/temp of the shower, it would always go cold.

 

[OvertonPlumber]

Intergas boilers do suffer from cold hex scenario. For example the dhw works a lot better if you have had your heating on and there is latent heat in the main exchanger. Yes the hot water will work on its own but your heating the entire block to heat the small dhw pipe. Oh my god the extreme's are noisy they have been likened to a s2000 on startup.
Have you any form of scale prevention? Combimate can stop them scaling up, I have a 12 year old one on my books, I've had to descale it twice now. First telltale sign is the boiler will goto 3 during hot water demand as the heat isn't being drawn away fast enough..

Is the cold water inlet fully open? They don't have flow control, you literally have to limit the flow with the inlet isolator to set your flow rate. Try closing it a bit water will go red hot!!

 

[dilalio]

What are the dynamic gas pressures at the meter and at the boiler inlet test point?

Before we start sl@gging the boiler off!

Was going to say, after reading to the end of all this... I am wondering about the gas supply!

 

[tfspark]

@OvertonPlumber got to agree with how noisy this boiler is when running hot water. Pretty quiet when heating is on. I had the boiler moved about six weeks ago from in a bedroom wardrobe onto the land at the top of the stairs. Mainly to free up space, but also to move the noise eslewhere! And no, these problems were there way before the boiler was moved.

At installation it was fitted with an Instinct by Scalemaster electolytic scale inhibitor. An Intergas engineer did comment once that he didn't think it was big enough. When the boiler was moved it was also fitted with a Hydro Path Pearl electronic descaler. I believe they are approved by Intergas.

When you say the boiler will go into 3, is that the digit on the right of the display. (I always wondered what they meant). There's nothing like that when running hot water.
I'll try restricting the cold flow into the boiler. I have restricted the hot into the bath so the wife can get a hot bath but all tests done in this thread were full flow into the bath. One of the reasons I bought an Xtreme 36 was because of the high flow dhw. If I'm restricting the flow that seems to defeat the point of the boiler. Could have had something smaller and cheaper!!

 

[tfspark]

@dilalio thanks for your reply. As far as gas goes I have no way of testing that. All I can say is that the gas leaves the meter in 28mm and arrives at the boiler in 22mm. We have a gas hob in the kitchen and a gas fire in a living room.
Since the boiler move it is now nearer the meter. The meter is under the stairs and the boiler is at the top of the stairs so it's not as if it's the other side of the building. I was assured during the original installation that the supply was sufficient.

I did have a new gas valve fitted not too long after installation because of delayed ignition. Fitted by an Intergas engineer so I've got to assume he set it up, or perhaps they come factory adjusted.

 

[Johntheo5]

I think you should contact Intergas and find out exactly what the DHW rated output is, the published DHW flow at a dT of 35C is 14.5LPM which requires a boiler output of 14.5*60*35/860, 35.047kW, so do you have a "36" kW boiler or not.

The other problem is the shower going cold which may or may not be the shower, when you say cold do you mean cold as in mains inlet temp or lukewarm cold?, even if running at its rated flow of 16.0LPM then the outlet temp (boiler output 29.0kW) should still be almost 36C from mains at 10C, it would just mean that the thermostatic element would shut off the cold mains to give no mixing, at least that's what should happen IMO, your replacement parts might cure this, if in fact it is a shower problem.

 

[tfspark]

The shower goes mains inlet temp cold, not luke warm, and it's quite sudden not a gradual drop in temp. As it's digital I'm suprised it doesn't give an error and shut down. Something like "insufficient hot water". It just stays cold until you turn it off.
It of course has an app and you can monitor a diagnostic page as its running. Shows hot & cold valve positions, hot water temp etc. I have been recording a video screen grab whilst in the shower but it hasn't faulted the last coulpe of times. I want to catch it faulted, leave it running and see what the diagnostic screen says and whether the boiler is still running.
Today I used the shower settings to set a flow rate of 10 lpm and a temp of 40°. The shower was ok, hot enough but just not enough water for my liking.

I'll try and speak to Intergas technical in the next couple of days.

 

[Johntheo5]

Wonder if that shower is a bit too clever and just shuts off the hot supply if the requested temperature is either a certain number of degrees both below or above the requested temperature, maybe set the shower to maximum flowrate and temperature say ~ 16LPM & 45C and see what happens, if 16LPM is achievable then the shower temperature will be 36C, see what happens, also see what those "hot & cold valve positions" show on your app, whatever they are. Not sure if you did measure the max flow from the shower?

 

[dilalio]

@dilalio thanks for your reply. As far as gas goes I have no way of testing that. All I can say is that the gas leaves the meter in 28mm and arrives at the boiler in 22mm. We have a gas hob in the kitchen and a gas fire in a living room.
Since the boiler move it is now nearer the meter. The meter is under the stairs and the boiler is at the top of the stairs so it's not as if it's the other side of the building. I was assured during the original installation that the supply was sufficient.

I did have a new gas valve fitted not too long after installation because of delayed ignition. Fitted by an Intergas engineer so I've got to assume he set it up, or perhaps they come factory adjusted.

Ah!
As always with threads on here...
"The plot thickens!"
With all the 'professionals' you've had out to see this system and ancillaries, I'd expect at least one of them to identify "if" there is a fault, and how to rectify it.

 

[dilalio]

Wonder if that shower is a bit too clever

Or is a bit too 'energy efficient'!
We all better get used to playing second fiddle to the environment!
Decrees have now been passed on how hot or cold something should be... Adapt or die!

 

[OvertonPlumber]

The most important factor and forgive me if you have already stated it, is the pressure and flowrate of the incoming water main.
Amount of time I see and I have been guilty of installing big combis on poor mains. There's quite a pressure drop through the intergas dhw pipes they won't really work properly without at least 2 bar of pressure.
Also remember the water main should always go direct to the boiler and it should not be piped up like another tap in the system.

 

[tfspark]

Ah!
As always with threads on here...
"The plot thickens!"
With all the 'professionals' you've had out to see this system and ancillaries, I'd expect at least one of them to identify "if" there is a fault, and how to rectify it.

Not sure how “the plot thickens”. If you’re referring to the replacement gas valve that was done over three years ago. I had a few problems with the boiler in the first year and had to get Intergas to repair under warranty. They were the only ‘professionals’ I could call on.
I’ve alway thought from day one that there wasn’t enough hot water at the bath. All this has only come to light because the Mira engineer suggested the boiler wasn’t producing enough hot water.
You say “if” there is a fault. That’s the whole point of the thread. I’m trying to establish if there is or not.

Maybe my smart shower is not as smart as I thought it was.

 

[mcmoby69]

I was under the impression that showers were limited to 12l per min?
Might be misinformed?
A 16l/min shower is achievable with an unvented cylinder but a combi?...mmmmm.

My old 1930's stop tap was recently replaced by United utilities, for a modern plastic one.
Before the swap I had 15l/min now I only have 12l/min .
Prior to the swap, no issues with the two showers going and a dishwasher/washing machine.
Now, the showers drop off noticeably.
I suspect they are designed to reduce water consumption. Especially when water meters are involved too. Another major restriction on water supplies are balofix valves and flexi pipe connectors.

So...... if the shower doesn't get it's required water flow it gets too hot, throttles down the supply temp which in turn causes the boiler to warm up too, which has ntc's and a water turbine which measures flow rate, which in turn modulates fan speed which reduces the burner.....etc etc etc.
A lot of complicated sh1t to make taps hot.
Just my back of fag packet thinking, no fancy calcs.

 

[Johntheo5]

Most combi boilers are perfectly capable of flowing 16 or even 20LPM but are regulated to match their thermal output, normally to give a dT of 35C
A 20kW combi might be regulated to 8.2LPM, a 30kW to 12.3LPM, a 36kW to 14.7LPM, a 50kW to 20.5LPM, regulation helps to avoid manufacturers getting, in their view, "silly" calls from people with say a unregulated 30kW combi filling a bath at say 16LPM and wondering why the HW temperature is only 35/36C or even lower in the winter which is perfectly understandable especially if they had just thrown out their lovely 50 year old vented copper cylinder with a 3kW heating element that had no problem in supplying HW at 20LPM at 60C no matter what the mains temperature was/is.