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Good evening, Brian is offline and the question has been past to me to answer for you
With the system you have described the two most common causes of tepid water is either the temp set on the boiler is not sufficient or the timer for how long the boiler should heat the Mega Flow for is not sufficient based on the demand.
Start by checking the timer for the hot water, how long is it set to run for?
Hi Andy, it depends on the type of timer in place.
Most installs would have the timer located next to the Mega Flow, locate the timer and tell me the make and model and I can talk you through checking the current settings and increasing the time the water is heated for.
Yes that device is the timer, it is dual purpose control your central heating and hot water.
To view the timer setting for hot water, move the slider on the right hand side up to the setting marked 'Hot Water'
Looking at the slider going from left to right, Hot Water is set to continuous so being heated all the time regardless of the program, have you recently moved it to this setting or was it like this when you were experiencing tepid water?
Ok now we have established the boiler is running all the time to heat the hot water, the issue is likely to be one of three issues.
1. The diverter valve which lets the boiler water flow around the mega flow has started to fail\not fully opening
2. The high limit stat on the mega flow is telling the boiler the temp is too high and does not require heat
3. The boiler is not heating the water to a sufficient temp.
In image 0910 it shows a pipe on the left hand side going into the bottom of the mega flow then going virtually up for about a foot then going into the reset of the heating circuit, there is a valve actuator connected to the pipe going into the mega flow (about 6 x 3 inches in size), on that there should be a small metal leaver, its sprung so you will need to apply pressure, you want to move that leaver and lock it in the far position (normally there is a lug the switch clip into to keep it in place), this will open the valve. Run the hot water tap for 5 minutes check the temp, then leave it for 30 min, and run the hot water tap again and see if the water is getting hotter.
Let me know how you get on.
Shut the leaver off after you have checked the water a second time (give it a good half hour or more). However do not leave the leaver in the locked position for more than a hour and a half.
Its none of those, ill send you a pic showing you what your looking for.
See valve circled in red to the left hand side of the tank.
Its hard to tell from the picture but that large box circled is a valve actuator which a valve under it, there should be a leaver on the metal box.
It should look like the valve here.
Do you need any further assistance