Hot & cold shower?

[Jaybee 45]

Hello,

I have an Ariston Genus 30 combi boiler 8 years old. We have had a problem for a few months with the hot water not constant when taking a shower. ( hot then going gradually to cold whilst we have to dodge in and out of the flow Brrrrr! ) I thought it was only happening to the shower but I have checked and it is the same from all taps.

I have checked the boiler and notice that when the hot water is being run the boiler fires for about 25 seconds and then goes out for about 10 seconds before firing again for 25 seconds etc. This accounts for the time we notice that the water in the shower goes hot and cold.

I may be wrong but I thought that when the hot water was being drawn the boiler should be firing all the time. The same thing is happening when the heating is on, the boiler stops and starts intermitently even though the room temperature hasn't been reached.

Any suggestions welcome please, so that I can have a nice long uninterrupted hot shower without goosebumps !!

 

[Softus]

Turn up the boiler thermostat?

 

[Jaybee 45]

Hi,
I've turned the Hot water knob and the Heating system thermostat to the highest setting. The boiler now goes up to 80 degrees C ( Max ) and still goes out when it reaches this temp. Although the water temp is hotter it still is not a constant uniterrupted flow and still goes hot and cool cos the boiler is not firing continuously.

Was this what you meant by turning up the boiler thermostat? Sorry I'm a bit green

 

[Jaybee 45]

Hello,

29 views and only one reply? Is this a major problem?? I am a bit worried because I've turned the thermostats to the limit and I'm probably wasting a lot of energy now. Would appreciate any advice on what to do next.

Thanks in anticipation

 

[kev25v6]

A new hw thermister seemed to sort out my boiler with the same problem. (different make of boiler though but still a combi)Try running the shower at a slower rate with the temp on the boiler a bit lower. I found this helped it to not cut out as much untill i could get it fixed.

 

[DP]

Check thermistor, but I would bet the problem is due to sedimented system. Chemnical cleanse and power flush is the answer.

Plenty can be found on this topic if you care to do a search

 

[kev25v6]

Check thermistor, but I would bet the problem is due to sedimented system. Chemnical cleanse and power flush is the answer.

Plenty can be found on this topic if you care to do a search

A lot of people seem to mention clean and power flush as a cure for all boiler problems. When i drained mine the water was pretty clear and after advice on here about the heat exchanger being blocked up with limescale and the like i had someone remove it to clean it out hoping to sort out some problems only to find nothing wrong with it. Power flush seems like just changing the oil on a car in the hope that it will cure all the running problems when really its the air filter thats the problem. Cleaning your system will most likely help it last a lot longer just like changing oil in your car does but i wouldnt get your hopes up that it will sort out your problem

 

[Jaybee 45]

Thanks for the replies.

I am just about to hire a powerflush machine for someone I know to flush out the rads as they definitely have sludge in them so do you think this will solve the problem with the hot water too? After flushing he is going to fit a magnaclean to the system. I hadn't connected the two problems before you suggested it could be due to muck in the system. Hope this will solve all the problems.

I must have been typing this as the last posting was made. I definitely know that there is sludge in my rads as they have large central cold spots and the water is black when I try to bleed them.

 

[DP]

Just because the water is clear, does not mean there is no sediment. Sediment has a tendency to settle at the base of the radiator. To remove this, you either take the radiator off the wall and tip one end over a tray to catch tar like water or use a power flusher as recomended by the makers. Chemicals may also be required to clear out what the power flusher does not remove. Obviously if someone does not understand power flusher capabilities, there is little chance of removing sediment that is 'beyond' the reach of fast flowing water.

The reason why water at tap will constantly alternate between hot and cold is either due to knacked thermistor (already mentioned), or sediment impeding flow of primary water through the plate heat exchanger.

The primary heat exchanger heats primary water. Thermistor monitors water temperature. This heated primary water imparts heat to cold water that is flowing through the secondary heat exchanger. If the secondary heat exchanger does not trasfer sufficient heat to water flowing out of the hot tap, thermistor monitoring the primary temperature overshoot, reduces flame size or even shutting the burners down until priumary temperature cools sufficiently.

By this time the water at the hot tap is getting cold. Burner fires and water at the hot tap starts to get hot until the burner shuts down.

To be successful at this game called fault finding, one has to first understand how a system works. If this knowledge is lacking, next best methosd is to have a box full of parts and start changing one after the other.

One side of the hot water heat exchanger will always be clean. It is the 'blackened' ports that cause the problem

 

[DP]

kev25v6, did you carry out water analysis on the system water? What was the iron content of system water. Just because you drained the system and water was clear means nothing as sediment is in sludge form at the base of the radiators.