From the United States of America? - Checkout our specific plumbing forum for you:USA Plumbing Forum

Discuss Combi boiler producing milky slimy water in the Central Heating Forum area at PlumbersForums.net

We recently installed a new Gloworm combi boiler in a property and we had a call from the customer to say that when he runs the hot water it comes out a milky colour and feels slimy. Also when he runs the cold tap the boiler fires up and then goes off. This is happening at every outlet. Even when the the washing machine pulls cold water in.

I've been there to check things and can confirm what he has reported.

My question is that has anyone else ever come across this and if so what id the cause / solution.

Oh and Gloworm have been out but not helpful at all. Just basically did what i did when i visited
 
Have you fitted a shock arrestor?
Did you convert from an OV system?
Haven't fitted an arrester yet no but was thinking about that to stop the boiler trying to fire when the cold is turned on but more worried about the milky hot water to be honest

Yes was converted from open vent to combi
 
Last edited:
Wetroom Store - Official Forum Sponsor
This official sponsor may provide discounts for members
We recently installed a new Gloworm combi boiler in a property and we had a call from the customer to say that when he runs the hot water it comes out a milky colour and feels slimy.
A milky appearance is normally microscopic air bubbles. If so, if he leaves a sample of the water for a few minutes it will gradually clear as the bubbles rise to the top.

This happens because gases are more soluble in cold water than in warm water so the heating action causes the dissolved air to come out of solution and form tiny bubbles. The tiny bubbles scatter light, which gives the milky appearance. (Milk looks milky because the suspended droplets of fat scatter light.)

The slimey feel is more unusual. It's just possible that he's actually feeling the 'fizzing' bubbles. It's also possible that seeing the milky appearance is triggering his imagination. Either way, when the bubbles clear the slimey feel will probably go too.

If standing time doesn't clear the milky appearance, you can get a sample of water tested by a lab. Will cost about £30 IIRC and will settle the matter.
 
A milky appearance is normally microscopic air bubbles. If so, if he leaves a sample of the water for a few minutes it will gradually clear as the bubbles rise to the top.

This happens because gases are more soluble in cold water than in warm water so the heating action causes the dissolved air to come out of solution and form tiny bubbles. The tiny bubbles scatter light, which gives the milky appearance. (Milk looks milky because the suspended droplets of fat scatter light.)

The slimey feel is more unusual. It's just possible that he's actually feeling the 'fizzing' bubbles. It's also possible that seeing the milky appearance is triggering his imagination. Either way, when the bubbles clear the slimey feel will probably go too.

If standing time doesn't clear the milky appearance, you can get a sample of water tested by a lab. Will cost about £30 IIRC and will settle the matter.
Yeah thanks Chuck did think that its air bubbles as it clears after a few minutes but trying to explain that to a customer is easier said than done as he never had it before. Thanks for your help anyway mate
 

scott_d

Plumber
Gas Engineer
Could be the higher pressure DHW cleaning the scale off the insides of the old hot pipes?
Take a sample at the boiler to see if its the same
 
trying to explain that to a customer is easier said than done as he never had it before.
What type of boiler did he have before? If it wasn't a combi that's the difference. If it was a combi maybe the new one is more powerful so the temperature change is more dramatic.
 
What type of boiler did he have before? If it wasn't a combi that's the difference. If it was a combi maybe the new one is more powerful so the temperature change is more dramatic.
Was an open vent to combi conversion
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
all hot outlets produce the same white milky ?
 
That's why he's not seen the phenomenon before then. Previously, his heated water was stored at atmospheric pressure for long enough for the air bubbles to disperse.
We do loads of conversions but never had this before so why with this particular one ?
Post automatically merged:

all hot outlets produce the same white milky ?
Yes all outlets the same
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
all valves fully open ? have you tried just connecting the outlet of the boiler into a bucket to see if its a supply or outlet issue?
 
all valves fully open ? have you tried just connecting the outlet of the boiler into a bucket to see if its a supply or outlet issue?
i haven't as yet no but the boiler is next to the kitchen sink which is where the hot and cold was connected to so connecting a hose to the outlet probably wont be worth it will it ?

Haven't checked valves as yet but will do
 
We do loads of conversions but never had this before so why with this particular one ?
As long as it clears from the bottom to top and doesn't leave a scum or oily film on the surface it's almost certainly air. If it clears from top to bottom it's particulate matter, maybe dislodged limescale, (which might explain the slimey feel) and should be cleared by flushing.

As well as air naturally dissolved in the incoming supply, other possible sources include: (a) a faulty inline pump somewhere; (b) air trapped somewhere in the pipework, e.g. in a dead-leg that needs to be removed.
 
As long as it clears from the bottom to top and doesn't leave a scum or oily film on the surface it's almost certainly air. If it clears from top to bottom it's particulate matter, maybe dislodged limescale, (which might explain the slimey feel) and should be cleared by flushing.

As well as air naturally dissolved in the incoming supply, other possible sources include: (a) a faulty inline pump somewhere; (b) air trapped somewhere in the pipework, e.g. in a dead-leg that needs to be removed.
Good idea Chuck thanks. will do these tests first to see what I get. The limescale being dislodged sounds a big possibility. Thanks for your advice
 

Reply to Combi boiler producing milky slimy water in the Central Heating Forum area at PlumbersForums.net. Plumbing questions, answers, tips and tricks.

CorgiDirect - Discounted Corgi Related Documentation and Plumbing Supplies
This official sponsor may provide discounts for members
Wetroom Store - PlumbersForums.net Sponsor
Power Shower Booster - Official PlumbersForums.net Sponsor
Test4Less PlumbersForums.net Sponsor
Corgi Direct - Plumbers Forums Sponsor
uHeat Forum Sponsor - PlumbersForums.net
Bulk Workwear - Workwear Sponsor for Plumbers Forums
Plumbing Advice - Find Plumbers Jobs

New Posts Threads Members

Top