Megaflo - hot water feed not heating tank

Discussion in 'Plumbers' Talk' started by Marcus Hake, Feb 6, 2018.

  1. Marcus Hake

    Marcus Hake New Member

    I'm not a plumber, and would really appreciate some guidance if possible.

    I have a large unvented Megaflo cylinder (Heatrae Sadia CL250HE) for our 3-floor, 3-bathroom house. Always been fine since installation around 10 years ago. However, now I'm getting no hot water unless I use the immersion heater to heat the tank. Not a disaster, as I have that manual override available, but it's going to be costing me a small fortune in electricity.

    The boiler is functioning fine, it seems. The heating is acting as expected, and all indicators say that the hot water is, too. But when the hot water is on (I've even run it on constant for an extended period of time), the water in the Megaflo never gets hot.

    I've checked the hot water flow pipe, and it's very hot. The return pipe is slightly warm. I believe this is how it should be. But the top output pipe is lukewarm, at best.

    If I put on the immersion for a couple of hours - hey presto - enough hot water to last around 24 hours.

    I've had a plumber come to look, and he's suggesting replacing the zone valves. Does that sound reasonable? As far as I can tell, hot water is getting out of the boiler and making its way to the cylinder. I don't really see how replacing the zone valves will help, but I'm certainly not an expert. At around 70 quid per valve I'm not sure that's a sensible place to start.

    Any feedback or guidance would be much appreciated.
     
  2. The Teach

    The Teach Screwfix Select

    how many zone valves does the unit have ? there are variations on how these units are installed.A photo of the cylinder including the valve setup always helps ;)

    Have you tried the thermal reset button,have a look at the users instructions for location of reset button.

    should be an easy fix but has it been serviced ? you may have home breakdown insurance which includes plumbing/heating.

    these cylinders need to be serviced and repaired by a G3 qualified operative,easy job for them.
     
  3. Marcus Hake

    Marcus Hake New Member

    Thanks for the swift response. There are 2 valves, labelled 'hot water' and 'heating' - it's an S-plan system, my plumber explained to me.

    I will look at the manual for the thermal reset button - thanks for the suggest. And also check my insurance - excellent point that I hadn't considered.

    My main worry about the plumber's advice is that hot water is clearly flowing through the flow pipe at the times I'd expect it to (i.e. when the hot water is timed to be on), so I'm not sure what effect changing the zone valves would have. At first sight it seems like 140 quid wasted.
     

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