Domestic hot water

pete_26

Hi no the system is set up on timer house heating on twice a day,domestic hot water on demand so if you turn on tap hot water is supplied burner fires,the DHW has control stat which has been replaced also donestic hot water stat replaced, water is very hot for a few seconds when tap is opend then rapidly cools you can leave your hand under the tap.

pete_26

domestic hot water

Hi small problem regarding Combi oil boiler,hot water very hot when you run at first then cools to a point that you can leave your hand under the tap,i have replaced the domestic thermostat still the same,also replaced the control thermostat,can any one help.?

Brad White_110

That would seem normal

especially if you keep the boiler at temperature and store the exchanger volume "hot and ready" rather than fire it up from a cold start each time.

Do you have a toggle setting that allows "storage"? If that is the case, you will practically equalize the DHW and boiler temperature. Once flow starts the temperature naturally drops.

Brad White_110

Might just be a spike

when the flow switch just "makes" and she fires up rapidly then stabilizes under flow. The "hold your hand" part is subjective; do you have actually measured temperatures?

pete_26

No temps
but was thinking could it be scale build up in heat exchanger.?
Also the diverter valve works fine.

frank_25

HOT water

A pumped recirculating line from the end of the hw risers, back to the cw inlet with a good mixing valve would solve the problem.

Brad White_110

How old is the unit and what is your local water quality?

If the unit is reasonably new and/or the local water quality is also reasonable, I would tend to doubt that. How do normal conventioal water heaters fare?

Frankie Wrench's option makes some sense especially if you have a timer, but if this is truly an instantaneous it would be firing all the time. Maybe look into storage?

But if the unit has lime or scale and it is new, say less than a few years old, maybe it is time to look at either a softener or a different means of generating DHW.

ScottMP

Does it

stay cool or does it rise back up to temp. ??

If its the coil it would'nt come back, of course you could have to a high a preasure in the house and you've got to high of flow. Has this been a problem since installation ?

Scott

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pete_26

yes the temp rises back if left ,then very very hot at tap for 10 seconds then cools rapidly, i have changed the DHW STAT,CONTROL TEMP STAT,i think it could be scale build up in the heat exchanger the unit is about 7-9 years old.Water pressure is fine Quality is fine.

frank_25

i'mn thinking

Holby here. They require a constant 180* to hot side and constant recirc blended into cold side. They work especially well in large demand applications. For the single, dual family jobs, I use the Sparco. Just me choices. BWDIK?IJAP