Open vented thermal store pumping over

[Johntheo5]

You might increase the pipe stat to 90/95c and see what kind of circulation you get with gravity only after lighting the fire, you definitely should get circulation through the dump rad and maybe some through the store. Also check the F&E tank.

There should really be a cold feed teed in just after the store vent pipe, that should stop the pumping over.

 

[Johntheo5]

@cross thread You said: "...is it sucking down the solid fuel expansion ?". If the water level in the expansion tank rises above the height of the solid fuel expansion pipe - how do I tell if it is sucking? If I put my hand under it, will I be able to tell, or if I hold a piece a string, or something lightweight, will it suck up the pipe?

Immerse the store vent pipe end in a "glass" of water.

 

[cross thread]

Have you had chance to check if it’s sucking down the expansion?
my opinion is the thermal store is the negative point of the system and a second vent is causing the issue

 

[baldchris]

It always takes a while to build the heat up in the woodburner back boiler! So, I checked the dump, and that does heat up as the woodburner heats the water supply, as expected. When I adjust the pipe stat on the feed right next to the woodburner, this closes my normally open valve and diverts the hot water to the store, and the pump kicks in as well. Immediately, the cycling over into the f&e tanks starts.
I checked the f&e tank, and the water level does not reach the height of the expansion pipes, nor the overflow. Water is coming out of the thermal store expansion pipe into the f&e tank. I couldn't get any decent photos (the lens just steams up, lol!).
So, this, I think rules out the sucking down the expansion (which is a shame, as life gets a lot easier once I know why the issue is occurring...).

 

[cross thread]

Did you act check if suction is occurring on the solid fuel vent ? Or assuming it’s ok

 

[baldchris]

@cross thread Initially, I simply put the palm of my hand under the thermal store expansion pipe and it had no impact and the cycling continued. I've just tried with the glass of water suggested by @Johntheo5 , and it also had no impact, the cycling continued. It is very hard to see anything (I'm not sure there's anything to actually see, mind you), because the space is so limited - the lid on the f&e tank only lifts about 6 inches.

 

[cross thread]

Ok thanks for that, you show a photo of a pump that’s on the flow according to the label, is the direction arrow on the pump body pointing down

 

[baldchris]

I'm not sure that was my picture - was it the one posted by @Johntheo5 ?
I checked anyway - its pointing upwards / with the flow in the direction of the thermal store.

 

[baldchris]

Is it worth trying to lower the ballcock to lower the water level in the f&e tank - as mentioned by @oldbutnotdead earlier in the thread? What's the best way to do this - ideally I'd just have an adjustable part 2 ball valve like this one: https://www.ebay.co.uk/itm/385299677704
But it's never that easy... so, I'd rather not consider importing one from anywhere - adjustable, part 2 valves must be available somewhere in the UK, but for the life of me, I can't find one. Has anyone got a link to a standard, recommended, adjustable ball cock valve?

 

[baldchris]

There should really be a cold feed teed in just after the store vent pipe, that should stop the pumping over.

I've been trying to think this through today - but, apologies, I can't work out exactly what you mean and where to put the tee. Are you able to clarify for me? Can I ask why you think that will stop the pumping over?

 

[Johntheo5]

I've been trying to think this through today - but, apologies, I can't work out exactly what you mean and where to put the tee. Are you able to clarify for me? Can I ask why you think that will stop the pumping over?

Normally any open vent system has its own vent and its own cold feed like I showed in post #21, it may but only may help to install a dedicated cold feed to the T.store as shown. What is baffling is that there is no pump over with with the boiler circ pump running at max speed but there is pump over from the T.store pump running at minimum speed, it could point to some restriction in the T.store circuit pipework, so maybe worth checking this out.
If the fire is lighting now increase the pipestat setting to stop the T.store circ pump and immediately manually latch open the normally closed 2 port valve before the circ pump, this will now give the hot water two paths (gravity circulation), one through the dump rad and the other through the T.store.
If it is circulating through the T.store you may (but I'm not familiar with normally open 2 port valves) be able to manually latch shut the dump rad 2 port, this will then mean all the circulation is through the T.store, if any problems you will soon see it venting into the F&E tank.

I presume you have previously checked that the 2 port valve before the T.store circ pump is in fact opening when the pipestat stats it?.

I don't see any point in adjusting the F&E tank level, there is no overflowing?.

It always takes a while to build the heat up in the woodburner back boiler! So, I checked the dump, and that does heat up as the woodburner heats the water supply, as expected. When I adjust the pipe stat on the feed right next to the woodburner, this closes my normally open valve and diverts the hot water to the store, and the pump kicks in as well. Immediately, the cycling over into the f&e tanks starts.
I checked the f&e tank, and the water level does not reach the height of the expansion pipes, nor the overflow. Water is coming out of the thermal store expansion pipe into the f&e tank. I couldn't get any decent photos (the lens just steams up, lol!).
So, this, I think rules out the sucking down the expansion (which is a shame, as life gets a lot easier once I know why the issue is occurring...).

 

[baldchris]

Thanks for that explanation! This is where it becomes unfortunate... I think we used to have this dedicated cold feed, but about 3-4 years ago, we asked another plumber to help us try to solve the cycling over issue. He identified that the cold feed was likely superfluous and could be contributing to the problem, so recommended that the feed was removed. I've attached a photo, looking up towards the f&e tank - you can see the cap on the pipe. The other end is teed in just before the woodburner valve (which is just before the pump).
Obviously, removing the cold feed didn't solve the problem and we've put up with the issue since, but I'm pretty determined to solve it this year!

I agree with your statement, "What is baffling is that there is no pump over with with the boiler circ pump running at max speed but there is pump over from the T.store pump running at minimum speed" (as a layperson here, it is driving me nuts trying to understand this! I always play the game of 'what's the difference' to try and diagnose issues and this is no different - but the boiler circuit is almost identical! So, your other point, "it could point to some restriction in the T.store circuit pipework, so maybe worth checking this out." seems to be an important one.

I'll try to run some tests, as you suggest, but fire isn't started yet this morning, so it could take a little while to get back to you again.

 

[oldbutnotdead]

First trick might be to get the woodburner pump running while woodburner is cold and see what happens (valves etc set as if burner has achieved 75°)
Is the venting happening through the woodburner vent or the thermal store vent? (I'm assuming it's the thermal store vent)

 

[baldchris]

I didn't start the fire yesterday and it was too cold to get the pump running - it's a high temp stat, so only runs in the range 50 - 95 degrees. I've started it today and even at 50 degrees, the cycling occurs. For now, I've set the stat to 85 degrees simply to delay/reduce the flow to the thermal store, and I'm dumping to the radiator.
I did ring the company that put the schematic together, and they essentially just followed the Gledhill schematic and recommendations - so I'll give Gledhill a ring on the 3rd Jan, and see if I can get someone in to investigate the issue. He did suggest, that it might be worth reducing the diameter of the vent pipe from store to f&e tank from 22mm to 15mm. So if I did this, and perhaps changed the pump, and perhaps re-instated the cold feed, then perhaps the cycling may be prevented?? I don't know how you guys do your job - it would drive me crazy, lol!

 

[baldchris]

First trick might be to get the woodburner pump running while woodburner is cold and see what happens (valves etc set as if burner has achieved 75°)
Is the venting happening through the woodburner vent or the thermal store vent? (I'm assuming it's the thermal store vent)

Yes - the venting is through the thermal store vent.