New boiler nightmare

[DP]

I bet that old cast iron boiler would have tolerated those corrosive chemicals better than this new lightweight one!

I have successfully used x800 in both cast iron and low content SE boilers

 

[screamer]

Water is still overflowing with the pump on medium speed. I understand that the F&E tank is there to allow for expansion as the water heats up, but have no idea how much expansion is expected in a 150 litre system. I expect there is also an element of restricted pipework contributing to the pumping over. Should this be remedied by adjusting the ball valve to reduce the water tank level by a few inches?

be wary on what speed the pump is on, my dad did it on a boiler once and the guy who serviced it noticed and put it back to 3 as thats the boiler requirements (it was a combi boiler, if that makes a difference)
obviously the plumbers/heating engineers will know better.

 

[Madrab]

be wary on what speed the pump is on

See posts #40/41/42

 

[Hugh Jaleak]

'Overpumping' is a serious issue, each time you lose water from the system through the overflow, the F&E Cistern will top back up with fresh water, slowly diluting the inhibitor concentration in the system and introducing air, both of which are not good for system health.

It needs sorting, which can only be done by investigating why its happening, and either removing any possible blockage in the pipework, or if needs be, reconfiguring the pipework to provide a neutral point between the Vent, Cold Feed and Pump as required.

 

[Miseryguts]

Sorry, only just seen some of those replies -

"Overflowing and pumping over are different....As you ask, expansion of water between 20 and 80°C is about 2.7%, so 4 litre for your system."

By overflowing, I meant water exiting from the F&E tank overflow.
Taking 4 litres as the estimated expansion (=.004m3), I estimate the tank width and length is about .4m x .5m, so the rise in level due to expansion should be in the region of .004/(.4x.5) which is .02 (20mm). However, it still overflows with only 4 out of 16 radiators turned on, when the expansion should be much less than that, or virtually negligable.

The attached photo shows the level in the tank with the system cold, although you can probably see that I have just bent the float arm to lower it a bit. I haven't actually witnessed it pumping over from the vent pipe, but I guess that's what is happening.

I haven't been back since, so don't yet know if that has cured it, but surely lowering the level enough to accommodate the pumping over should fix the issue (albeit not ideal having hot water going into the tank)? Doubt there's any chance of getting the plumber back now that he's been paid.

 

[fixitflav]

It needs sorting, which can only be done by investigating why its happening, and either removing any possible blockage in the pipework, or if needs be, reconfiguring the pipework to provide a neutral point between the Vent, Cold Feed and Pump as required.

Agreed, that's why I asked for a sketch of the layout.

 

[fixitflav]

By overflowing, I meant water exiting from the F&E tank overflow.

OK, I got that wrong. Interesting. Can you catch and measure the water which overflows on each start-up? That amount must be getting into the primary circuit. The question is - how and where?
As you say, the level rise in the F/E tank due to expansion should be minimal.

 

[Miseryguts]

Sure, I can go back and sit in the loft with a bucket for however long it takes: I already asked my mother to leave a bucket under the overflow pipe so we could see how much we are talking about, but it keeps bloody raining!

The system was not originally designed as an S-plan layout and that in conjunction with the known flow restriction (which we spent £580 on powerflushing) is likely to be causing it to pump over.

Perhaps a complete solution would be to add something else to accommodate the pressure, or even raise the F&E tank, but is there a good reason why I cannot simply lower the water level in the tank?

 

[Madrab]

is there a good reason why I cannot simply lower the water level in the tank?

Not really, as long as there is enough water level to allow the system to breather then it should be fine.

As the system starts the level can drop a little as the pump pulls water down and then as it heats the water expands and the level in the cistern will naturally rise and then drop back down again when it cools.

 

[fixitflav]

Sure, I can go back and sit in the loft with a bucket for however long it takes:

Does it overflow continuously when heating's on, or rise up and overflow, and then drop back, or what? (apologies if you've already said, it's a long thread!)
If water's going out it must be coming in, have you any idea where? Have you tried shutting off the mains feed to the F/E tank and see what happens?

 

[fixitflav]

I haven't actually witnessed it pumping over from the vent pipe, but I guess that's what is happening.

If you can't manage a system sketch, it's at least worth checking where the connections are. The modern way is Boiler - Open vent - Cold feed - Pump - Rads, but if it's an old place it might be Cold feed - Boiler - Open vent - Pump - Rads (or possibly pumped return, with a few more options).
If the open vent connection is after the pump that could cause pumpover, a bad thing (but not necessarily overflow).

 

[Miseryguts]

I'll go and see what happens over a complete heating cycle in the next couple of days.

If you can't manage a system sketch, it's at least worth checking where the connections are. The modern way is Boiler - Open vent - Cold feed - Pump - Rads, but if it's an old place it might be Cold feed - Boiler - Open vent...............

Thinking about it now, you may well have a point about the connections:- It seems the original gravity system was modified for the previous floor standing boiler installation, which used a 2 port valve next to the hot water cylinder; however, heating and water could not be controlled independently due to no cabling to the wiring centre (see previous posts), which is why the plumber ended up fitting a wireless hot water thermostat controller for this new boiler. Now I realise that the DHW 2 port valve has been moved downstairs (perhaps it needed to be next to the wiring centre), so the pipework has been altered and that may be causing pumping over that never used to occur.

Will try to assess the layout next visit.

 

[Miseryguts]

So to hopefully conclude this thread: lowering the F&E tank level by a couple of inches appears to have stopped it overflowing on start up, although I suspect there must still be an element of pumping over.

I am attaching a photo to show where the new (white) 2 port valve is in the circuit, as opposed to the previous location upstairs near the DHW cylinder. I'm not certain which is the open vent pipe, but seeing as the F&E tank is 2 floors higher than the boiler room, I don't feel there is an issue with air getting into the system, since it sounds quiet when running and there is inhibitor in there.

I'll post updates if anything changes, but in the meantime, thanks to everyone for their helpful advice. This has taught me the importance of checking details of a new boiler quote before giving the go ahead!

 

[fixitflav]

although I suspect there must still be an element of pumping over.

It either is or it isn't, it's not hard to check, and if it is, it needs stopping!

I am attaching a photo to show where the new (white) 2 port valve is in the circuit

Can't tell a great deal from the photo. I assume the pump is pumping upwards, and the other white pipe into the suction is the cold feed.
The bronze coloured tee above the pump - does it have a pipe straight up from it, or is that just a shadow and the tee is blanked? If it's the vent pipe, no surprise there's overpumping. Or is the pipe after the tee, before the motorised valve the open vent? In either case, the level in the vent pipe rises by the same as the rads (or cylinder) headloss, so overpumping is a strong possibility.
Moving the open vent connection to the pipe from the boiler, before the tee would stop it.
You can find out more what's happening by feeling which pipes get warm when.

A similar problem in this thread https://www.diynot.com/diy/threads/can-i-reverse-my-ch-hw-pump.623085/post-5659774