DHW not getting over 60 deg

[billm]

Hi, my Ariston Genus 27 mffi CH Boiler is now 10+ years old, and for a while now I've noticed the upstairs shower is not running as hot as it used to even when there is no other HW being drawn in the house. At first I thought it was due to heat losses of the non insulated 15mm pipe feeding upstairs as it does go the long way round, but that hasn't changed since it was installed so it can't be that. And it's all inbuilt so I couldn't get to those pipes to insulate them anyway.

I then ran the HW at the kitchen sink which is very close to the boiler, hot tap only full on for 5 mins, and although it felt hotter than upstairs the temp indicators on the boiler wouldn't go over 60 (see attached) even though the temp dial is on max, which I waggled just incase it was iffy.

I assume the DHW should go much hotter ?

I've worked out, via Google, the DHW circuit within the boiler. The water from the Primary Burner is directed by the Diverter Valve (which is working) through the Secondary Heat Exchanger monitored by a DHW Temp Sensor and of course the PCB circuit board controls the lot.

Is there a way of determining which of these is at fault or is it case of swapping out the cheapest, presumably the Temp Sensor first, then the Secondary Heat Exchanger, and lastly the PCB, until the problem is resolved ?

I haven't noticed any issues with the CH, just the DHW.

thanks

 

[Dan Robinson]

Google Mass flow rate.

 

[DH6]

Employ a heating engineer to diagnose the fault accurately!

 

[billm]

Employ a heating engineer to diagnose the fault accurately!

thankyou

 

[D_Hailsham]

Google Mass flow rate.

I did; and got this:

In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units.

How, exactly, does that answer the OP's question?

 

[Dan Robinson]

I did; and got this:

In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units.

How, exactly, does that answer the OP's question?

Because it will help them answer the question.

Haven't forgotten about you vanishing from the other thread either.

 

[JohnD]

When did you start to notice this?

In winter, the hot tapwater will be cooler, because the incoming supply is colder.
For example, if the boiler heats the water by, say, 40C, and in summer the supply is at, say, 10C, your tap will run at 50C. In winter, if the supply is at, say, 5C, your tap will run at 45C.

If you turn the tap down from max, the temperature is likely to increase, because the boiler is not trying to heat so much water.

I think it would be useful for you to test the tapwater with a thermometer rather than saying it feels warmer or cooler.

 

[billm]

When did you start to notice this?

In winter, the hot tapwater will be cooler, because the incoming supply is colder.
For example, if the boiler heats the water by, say, 40C, and in summer the supply is at, say, 10C, your tap will run at 50C. In winter, if the supply is at, say, 5C, your tap will run at 45C.

If you turn the tap down from max, the temperature is likely to increase, because the boiler is not trying to heat so much water.

I think it would be useful for you to test the tapwater with a thermometer rather than saying it feels warmer or cooler.

Hi, I was aware of the shower alternating Hot & Cold during the winter about 2 years ago so I took the secondary heat exchanger off and gave it a soak with a kettle descaler. I think it made things a bit better as I'd forgotten about it until recently when I noticed the shower isn't all that hot even when turned fully up. It probably has something to do with the temperature rise of the boiler and the efficiency of the exchanger which is why it's noticeable in winter and not in summer.

The DHW thermostat must be OK as it's capping the temperature to the recommended 60deg in the boiler.

After 10+ years I guess a new secondary heat exchanger at £40 and 1/2 hour to fit it won't go amiss.

Either that or I'll ask a heating engineer to fit a new Mass Flow Rate sprocket ..

 

[Steelmasons]

Either that or I'll ask a heating engineer to fit a new Mass Flow Rate sprocket ..

 

[Agile]

Because of the risk of scalding boilers are usually designed to not allow DHW to significantly exceed 55/60 C.

Many boiler temperatures indicate the circulating water temperature and not the actual DHW temperature which is lower by 10-20 C.

Tony

 

[DP]

Billm, all boilers are designed to heat the cold water (for delivery at hot tap) by 35 degrees C if the gas rate and flow rate of hot water are as specified by the makers. Usually 24kw will deliver about 9.8l and 28kw about 10.5l

As per earlier example, cold water at 5 degree C will be delivered at the tap at 40 degree C when tap is at full flow ( flow rate being specific to boiler HW delivery)

 

[billm]

Billm, all boilers are designed to heat the cold water (for delivery at hot tap) by 35 degrees C if the gas rate and flow rate of hot water are as specified by the makers. Usually 24kw will deliver about 9.8l and 28kw about 10.5l

As per earlier example, cold water at 5 degree C will be delivered at the tap at 40 degree C when tap is at full flow ( flow rate being specific to boiler HW delivery)

Hi, I know the Gas pressure is fine as it was tested recently and I assume the water pressure is more than adequate. So is it a feature of all Combis that in winter when the incoming water temperature is lower, say 5 deg, that the DHW will be cooler than in summer on full tap and that the way to counteract this is to reduce the flow rate at the tap in winter to compensate. Rather than it being a fault of the boiler ?

If I measure the temp at the kitchen hot tap and it's 60 deg, or thereabouts, can I assume the secondary heat exchanger is working OK?

The boiler hasn't been serviced for years. With regard to my symptoms what would be the elements of a service that could cure this "problem" other than ensuring all the gas jets are open on the primary heater ?

thank you

 

[billm]

Because of the risk of scalding boilers are usually designed to not allow DHW to significantly exceed 55/60 C.

Many boiler temperatures indicate the circulating water temperature and not the actual DHW temperature which is lower by 10-20 C.

Tony

thanks Tony, I probably need to measure the DHW at the tap

 

[DP]

Billm, a service, preventative maintainance, is essential.
When called to carry out this task, I would clean the main heat exchanger matrix, pressurise the expansion vessel, clean the burner, clear out combustion chamber plus other tasks specific to the boiler model

By gas pressure I mean the burner pressure at full power. Gas pressure should always be fine, but undersize gas pipe could account for lower burner pressure.
Water flow rate- run hot tap at full flow, collect water in a suitable container over 15 seconds, measure the collected quantity, times four gives you hot water delivery. You should get 9.7/ 11.4 litres for 24 or 28kW medals respectively. Flow regulator within boiler being faulty could account for flow issues

If the LED display is indicating 60, I suspect you will exceed above quantities

 

[billm]

Billm, a service, preventative maintainance, is essential.
When called to carry out this task, I would clean the main heat exchanger matrix, pressurise the expansion vessel, clean the burner, clear out combustion chamber plus other tasks specific to the boiler model

By gas pressure I mean the burner pressure at full power. Gas pressure should always be fine, but undersize gas pipe could account for lower burner pressure.
Water flow rate- run hot tap at full flow, collect water in a suitable container over 15 seconds, measure the collected quantity, times four gives you hot water delivery. You should get 9.7/ 11.4 litres for 24 or 28kW medals respectively. Flow regulator within boiler being faulty could account for flow issues

If the LED display is indicating 60, I suspect you will exceed above quantities

Hi, I measured the Hot water at the Bath tap fully open just now and it's 3L per 15 secs so that's 12L per min. Sounds about right give-or-take.