Megaflo problem?

CDS412

Any diagnostic geniuses out there? Hot water is running cold but CH seems ok. Hot water had been ok but noticed pressure dropped back a little after tap first turned on.(coincidence?) Went to check air gap and with mains turned off, water will just not stop running from hot tap and overflow, when PRV opened, after 15 minutes. With PRV closed, overflow stops. Seems like I have a problem. No pressure gauge on system, which should operate at 3 bar. Have switched heating off as concerned it may not be safe to operate. Gas boiler heat source was only installed new two years ago and hasn’t given any problems previously. I’m assuming it’s the Megaflo that’s the problem but wondering if it’s safe to operate the CH in the meantime? Any ideas out there? I’m assuming it’s a job for a qualified engineer but any pointers as to where the problem may be would be helpful....thanks.

fezster

If you have good flow from the hot tap, then it's not your Megaflo air bubble. There are instructions on the side of the unit on how to replenish it, if you need to.

Can you see the flow pipe from your boiler going to the cylinder? With only hot water on at the programmer, does this pipe get hot? Then check the return pipe from the cylinder - does this start to warm up gradually after 5 mins of the boiler being on? Check the motorised valve on the cylinder flow is opening if both of the above are not getting hot.

I'm not sure what you mean by "overflow" in your post. The TPRV on the side of the cylinder should not pass water under normal circumstances. When replenishing the air bubble, you hold it open. You'll have a separate PRV on your incoming cold water supply - is this what you mean is "overflowing"? If so - do you have a pressure reducing valve on your incoming cold supply?

CDS412

Managed to get a Scottish Gas Engineer. She diagnosed a faulty mixer cartridge in one of the sinks which was allowing cold mains round the system at higher pressure than the hot water. Megaflo and boiler are tip top. Problem disappeared after she started to explain it, which means it could come back again.....but a plumber required, if that happens. Thanks for responding. Much obliged.

fezster

I had the same problem - easy to confirm as you just turn off the valve coming from your hot water cylinder, and then run any hot tap. It should immediately stop flowing water. If cold water is coming out of it at some pressure, then the cold is passing somewhere (as in your tap's case, in my case it was a shower thermostatic mixer).

The shower thermostatic valve has non-return valves to stop this happening. A common problem is debris getting stuck in these causing them to remain open. I managed to get access to it and flush it with water to clear it up - problem solved.