Intergas combi hot water temperature

[tfspark]

I have a four year old Intergas Xtreme 36. I have the dhw temperature set to 65°C.
I know not to expect that temperature at the taps but I'm wondering what the temerature should be?

At the kitchen sink I have a flow of 7.7 l\min with a temp of 56°.
At the bath I have a flow of 11.1 l/min with a temp of 47° (from day one of installation wife complains bath is not hot enough)
At the shower I have a flow of 12.25 l/min and a temp of 45°.

Clearly the higher the flow rate the lower the hot water temperature at the taps but should I really expect a drop of 20° at the shower?

This question is prompted by a (ongoing) problem with my Mira Activate digital shower.
Any advice or suggestions greatly received.

 

[Stuckinarut]

What temperature is the incoming cold main? If it’s say 10 degrees then you should be getting approx 45 degrees coming out with a flow rate of 14.5 lpm. If it’s 15 degrees, then you’ll be getting 50 degrees with the same 14.5 lpm flow rate.

So, the lower the flow rate the higher the hot water output temperature. This is the same for any combi boiler I know of.

 

[tfspark]

Thank you for the swift reply.

Yesterday I measured the cold water temperature at 11°C. So at 14.5 lpm I should get 46°C. As the shower flow rate is 12.25 lpm I should be getting better than 45°. Is that enough difference to say there is a problem with the boiler?

Just to expand on the shower problem.

Mira Activate digital shower, dual outlet, rear fed. In January the problem started where the shower would reach temperature and stay fairly constant for a couple of minutes then go freezing cold. It would stay cold until turned off. Would happen every time. Got Mira engineer round for a warranty repair.
He wasn't convinced it was a shower problem but lack of hot water from the boiler. He replaced the circuit board in the shower and it has been fine until last week. It is now intermittent and has happened three times in the last week.
Happy to get Mira out again but i know it won't do it while they're here so chargable no fix.

Just want to be sure it's not a boiler problem.

(perhaps the shower problem should be a seperate thread)

 

[Stuckinarut]

I would be checking for a failed mixer. Isolate the boiler cold water inlet and run the hot tap and try the shower, if you get any sort of water you have a failed mixer somewhere

 

[Johntheo5]

Depending on above test suggest....
If the shower is flowing 12.5LPM at say 40C and the combi is set to 65C then 6.7LPM at 65C from the combi should mix with 5.8LPM of mains water at 11C to give that 12.5LPM at 40C, (Boiler Output, 29.29kW), if the shower is not doing this continuously, then suggest setting the combi to 40C or nearest, set the shower to max temperature setting and check shower temperature and flowrate, see if temperature is continuous.

 

[tfspark]

Thanks for the replies, I appreciate it.

The shower figure quoted in my op was the hot water into the mixer box, not blended flow from the shower head. I disconnected the hot pipe into the mixer box and ran 10l into a bucket to measure flow. I also checked the temp with a temperature probe.

The problem at the moment is that it's intermittent.
I will certainly try both tests but if the fault is not present then I think they will be a bit inconclusive.

Thanks again.

 

[Johntheo5]

"At the kitchen sink I have a flow of 7.7 l\min with a temp of 56°. (Boiler Output,
At the bath I have a flow of 11.1 l/min with a temp of 47° (from day one of installation wife complains bath is not hot enough)"

Are these two taps just single HW taps and not on mixers?
Kitchen tap with a flowrate of 7.7LPM & 56C requires only a boiler output of 24.2kW, at 65C would require 29.0kW
Bath tap with a flowrate of 11.1LPM & 47C requires only a boiler output of 27.9kW, the maximum temperature should be 57.5C at the rated
36kW boiler output. OR a maximum flowrate of 9.56LPM at 65C (from mains at 11C). at the 36kW rated output.

Its relatively quite easy to see if the boiler is giving its full output, run the Hot bath tap and the kitchen Hot tap fully open, take a snapshot of your gas meter and exactly 3 minutes later (to the very second), take another snapshot, the boiler input will be the difference in readings X 11.0 X 20 kWh, should get ~ 41/42 kWh.

 

[Madrab]

I have an activate too - used to get variable temps - hot cold hot - sent me out a new flow temp thermistor, no issues since.

Outlet flow and temps will also be dictated by the length of the HW pipe run and how many elbows etc are in it. Flow is also determined by the outlet type.

 

[tfspark]

@Johntheo5 - The bath tap is a single HW tap, the kitchen sink is a mixer. I have done the calculation that you suggested twice and get two slightly different readings. First time was 33.44kWh and the second time 31.46 kWh. Not close to the 41/42 kWh you suggested?

@Madrab - it's kind of good to know that someone else had a problem with a Mira Activate. I'll ring Mira in the next couple of days, explain the situation, and hopefully get some sort of resolution. When it goes cold it doesn't matter which outlet is being used or what temperature it is set to. (Between 38° and 45°). There is probably about 15 feet of pipe, all 15mm, between the boiler and shower mixer. I think from the boiler there is two elbows, a tee, another elbow and finally a tee. (they could be 90° bends rather than elbows)

Both boiler and shower were fitted about three months apart in 2021 and the shower has been absolutely fine until January this year.
Can't say I've been too enamoured with the Intergas boiler. Had a few problems in the early days.

​

 

[Johntheo5]

@Johntheo5 - The bath tap is a single HW tap, the kitchen sink is a mixer. I have done the calculation that you suggested twice and get two slightly different readings. First time was 33.44kWh and the second time 31.46 kWh. Not close to the 41/42 kWh you suggested?

Assume these tests were done with both Hot taps fully open?
OK, at ~ 88% boiler efficiency this equates to between 27.68kW & 29.42kW, average output of 28.55kW, only 79.3% of its 36kW rating.
Still can't rule out some mixing somewhere so suggest just shutting the cold mains at the boiler and set the kitchen tap to fully hot and open it, should get no water, do the same with the shower, put it to fully hot and full flow, again should get no water out. If this test is successful suggest (after reopening the boiler cold mains) just repeating the HW bath test only with boiler set to 65C, measure the flowrate and mains cold and bath tap HW temperature. Your last bath test showed 11.1LPM at 47C, 27.9kW, (the temp should have been 57.5C at the boiler rated output of 36kw) very close to your average max boiler output of 28.55kW, so does point to a boiler fault if no mixing taking place, which you will be able to prove shortly if you do the test.
If you wish, also perhaps do that 3 minute gas consumption test as well while doing that bath HW test, that will remove all doubt?.

 

[mcmoby69]

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

Before we start sl@gging the boiler off!

 

[Johntheo5]

Of course.
There could be two problems, one is the above, apparently unable to achieve full output, for whatever boiler end problems, (except a 30kW model was installed!), the other is the shower problem running hot & cold.

 

[Madrab]

According to the specs the Extreme 36kw has a max output for HW @ ~32.7Kw @ factory settings - under ideal conditions it should deliver 14.5L/Min @ a 35deg rise. That is the ideal output, real world temps may not quite meet those level due to external factors.

If you incoming cold water is 11deg, then the boiler should deliver ~14.5L/Min @ 46deg @ 32.7kw (MAX). As the flow through the boiler is reduced, that HW temp rise will increase. Setting the HW temp @ 65deg won't make any difference to that output temp all it will mean is of the HW output temp reaches that set temp the boiler will modulate down to maintain it.

Taking the shower as the example - the shower will limit the output to a safe temp - it's part of it's design feature. Any hotter would constitute a scalding risk. The activate is factory set to 45deg. The bath output here is the real anomaly.

I would be very surprised if it did, given the HEX design, but does the boiler cycle on and off when the temp fluctuates? If it doesn't then I'd suggest it isn't the boiler at fault. One fault may be, as has been suggested, that there's a mixer that's passing cold into the hot circuit.

 

[Johntheo5]

One of the tests on the bath (non mixer) HW tap showed a flow of 11.1LPM at 47C from mains at 11C (DHW SP 65C).
Boiler output required, at 47C, 11.1*60*(47-11)/860, 27.88kW, if the boiler was producing its rated output of 36kW then the tap temperature should have been, 11+(36*860/60/11.1). 57.5C?, the test carried out with both hot taps fully opened gave a boiler output of ~ 28.55kW pretty close to the bath tap tests which gave 11.1LPM at 47C, 27.88kW.
Lets see what the next tests show up.

 

[tfspark]

Firstly, thanks to everyone who has taken the time to reply. I really do appreciate it.

Mixer taps - I was mistaken with the tap in the kitchen. It is not a mixer tap. It has a hot tap, a cold tap and a single spout. Sorry for any confusion. We do have a mixer tap in the downstairs cloakroom. I turned off cold to the boiler and ran full hot in cloakroom. No water.
I did the same with the shower. I set it to 16 lpm and 48°, both max. No water but very quickly tripped out with an error 50, "no flow detected" so unsure if that's a true test.

Today cold water into the bath is 10°C. From the hot bath tap I measured 11.3 lpm at 47.8°. Running the three minute test I beleive this works out to 28.97 Kw.
As @Madrab suggested the boiler install manual says DHW input rating is between 3.6 and 32.7 Kw. If boiler ran at 32.7Kw (unlikely?) then the temperature in the bath should be 51.5° if my maths is correct?

Gas - I don't know much about the gas side of things, so all I can quote is what is written in the service record. Not sure if that's is what is required.
At install, May '21, Gas rate = 3.34 m³/h or 35.99 Kw. Gas inlet pressure 20.4 mbar.
Last service record shows - at max rate: co 43 ppm and co2% 9.0. at min rate: co 27 ppm and co2% 9.2. I'm guessing that's flue related and not gas?

Shower - I have just spoken to Mira regarding the shower going cold (intermittently). First question was "how hot is the water going into the shower. It should be between 55° and 65°". (By my reckoning that requires boiler input of 43.5 Kw. Can any boiler produce that?)
I explained that it had happened before and a pcb was replaced in January. Also up until then it had been working fine for four years.
Rather than an engineer visit I said I was happy to fit any parts they thought appropriate. So I'm getting three parts sent in the next few days. I'm not sure if there are more than three parts in it!