Electric toilet syphon problem - advice welcome.

[Irish Rover]

I have 2 cheap as chips TMC electric toilets on my boat fitted in 2018. Originally they both had 19mm plumbing but one pump gave up a couple of years ago [with help from yours truly ]. I couldn't locate a replacement 19mm so got a 25mm pump and changed the fittings. That's all by way of explanation. The original 19mm is still working perfectly except it has started to fill with clean sea water when unattended. I have an anti syphon loop on it and I've played with that including washing it thoroughly in soapy water particularly the valve. Still sucking water. I do have a replacement 25mm loop and I swapped over the valve section from that - same size, same thread - but no difference. I've ordered a replacement 19mm loop which my wife will bring when she comes to join me on Saturday but I suspect it may not solve the problem since changing the valve didn't do the trick - the rest is just white plastic.
I'm wondering if there's something I'm missing - is there a cut off valve in the pump which has failed, for instance. I have a replacement 25mm pump and all the bits and bobs to change the whole lot if I have to but I'd really prefer not to, at least until I get back to home base in a good few weeks where I'll have access to good overalls and copious amounts of hot water for showing.

 

[Bilgediver]

If you have a working anti syphon loop between the seacock and the toilet then it should prevent clean sea water entering the toilet. If the toilet is filling with clean water then the air bleed into the antisyphon loop has become blocked and needs to be cleared.

The better layout is to have the antisyphon loop between the pump and toilet which ensures the pump is always flooded and does not draw air when operating.

Do you have a holding tank or do you discharge overboard? If the later then there should also be an antsyphon loop in the discharge line.

 

[VicS]

If you have a working anti syphon loop between the seacock and the toilet then it should prevent clean sea water entering the toilet. If the toilet is filling with clean water then the air bleed into the antisyphon loop has become blocked and needs to be cleared.

The better layout is to have the antisyphon loop between the pump and toilet which ensures the pump is always flooded and does not draw air when operating.

Do you have a holding tank or do you discharge overboard? If the later then there should also be an antsyphon loop in the discharge line.

ITYWF that electric toilets can be fitted with a solenoid valve on the antisyphon loop.
This means that the loop can be fitted between seacock and pump and will probably provide a more reliable syphon break when the toilet is not in use.

Jabsco 37068-2000 - SOLENOID SWITCH / Toilet Accessories / Marine Toilets / Marine / Xylem JabscoShop - Jabsco & Rule Pumps and more - from the experts

 

[Irish Rover]

If you have a working anti syphon loop between the seacock and the toilet then it should prevent clean sea water entering the toilet. If the toilet is filling with clean water then the air bleed into the antisyphon loop has become blocked and needs to be cleared.

The better layout is to have the antisyphon loop between the pump and toilet which ensures the pump is always flooded and does not draw air when operating.

Do you have a holding tank or do you discharge overboard? If the later then there should also be an antsyphon loop in the discharge line.

Loop is between the pump and toilet. I have a holding tank.

 

[Bilgediver]

Loop is between the pump and toilet. I have a holding tank.

In that case it. Sounds like the bleed hole at the top of the antis syphon loop is blocked so enabling the Syphon effect to draw water through the pump .
Do you have the solenoid valve mentioned by another poster?

 

[Irish Rover]

In that case it. Sounds like the bleed hole at the top of the antis syphon loop is blocked so enabling the Syphon effect to draw water through the pump .
Do you have the solenoid valve mentioned by another poster?

No solenoid and as I mentioned in my op I tried washing the valve and then changed it completely with no success.

 

[Irish Rover]

No solenoid and as I mentioned in my op I tried washing the valve and then changed it completely with no success.

Replacement loop arrived. Made no difference. Since everything worked satisfactorily for 4+ years I have to assume it's a problem with the pump. Will try to change the pump in the next day or two when I'm tied up somewhere less bumpy than Ermoupoli.

 

[rogerthebodger]

Is this the type of TMC head you have

https://m.media-amazon.com/images/I/71CIzpfu2mL._AC_SX425_.jpg

if so the flush pump is in the same housing as the pump out macerator.

I had one of these and it went rusty and stopped working

I replaced the pump out pump with an electric diaphragm pump and the flush pump with a seprate fresh pressure pump with 2 sperate switched so I can pump out and flush in which ever sequence I wish