Megaflow not heating up like it used to?

[Hairy Beaver]

Hi,

We have a wood burner that heats a thermal store, once this reaches 60c it pumps water through a heat exchanger that is connected to the main megaflow cylinder this should then heat the hot water until it reaches about 58c then a valve opens and the hot water coming from the heat exchanger goes to the rads.

The system has fitted by a relation who is a plumber but he lives at the other end of the country so i cant just get him back to look at it.

The problem seams to be that I have hot water 65c+ leaving the heat exchanger and going into the megaflow but it wont rise the temp of the megaflow hot water above about 54c The water returning to the heat exchanger after going through the megaflow is still almost 65c (I am getting the temp readings using a digital kitchen thermometer so they may not be very accurate)

It has been working ok up to last week when the motorised valve that lets the water from the heat exchanger enter the megaflow stoped working. I have replaced it and the new one is working.

Any pointers as to how I work out what's going on would be much appreciated.

 

[mountainman]

Sounds like a circulation problem.

When you changed the valve did you vent the primaries to the cylinder fully?

 

[Hairy Beaver]

Sounds like a circulation problem.

When you changed the valve did you vent the primaries to the cylinder fully?

Probably not?
I drained the system via a drain off point by the lowest radiator and then refilled by opening the filling loop, letting the water run through until it started coming out of the drain off then closing the drain off and letting the system fill until the pressure gauge came up the mark. I have bleed all the radiators but there was almost no air in them.

Thanks for taking the time to reply

 

[SimonG]

So just to clarify, you have a thermal store that feeds an unvented megaflo?

 

[Hairy Beaver]

I am not sure??
I'll try and describe in my best none technical way...
The boiler on the wood burner feeds into a cylinder this has a header tank above it. When the wood burner has heated the cylinder to approx 58c it starts to pump the hot water around a heat exhanger located between this first cylinder and the bigger megaflow cylinder.
The megaflow cylinder is connected to the other side of the heat exchanger, this water should be heating up the megaflow but is not doing a very good job of it at the moment.

Should I try draining and refilling the system?

 

[mountainman]

You probably have a partial air lock in the HW primaries.
Can you post some piccies of the cylinder connections and controls?

 

[Hairy Beaver]

Thanks for taking the time to look at this.
The black pipes on the right of the first photo are from the solar water system (that's a whole other story!)

Cheers,

Hairy Beaver

 

[mountainman]

I still think you've got a partial air lock.

From looking at the pictures I can't see any air vents on the pipework.
Furthermore, both of the pumps are fitted at the wrong angle, the rotors should be horizontal to stop air collecting in the head and ruining the bearings.

 

[Hairy Beaver]

Do you have any advice regarding getting rid of the air lock?

 

[Best]

When the system is cold, you could try slackening a nut slightly to release some air. Use an old towel for any water.
As has been mentioned, those pipes should have manual vents on them & the pumps should not have the motors pointing up.

 

[mountainman]

I would be inclined to fit air vents at accessible high points on the primary pipework.
As a quick fix though you could loosen a compression joint to the flow and return connections at the cylinder.