Hot water taps sputtering

[michcosg]

Hi Folks

I have a customer who is getting some sputtering on his hot taps, similar to that experienced when a system is attempting to clear air trapped in its pipework. The difference here is that it never seems to get rid of the air and the sputtering carries on indefinitely.

He has a Valiant combi boiler situated on his top floor with cold water to the the lower bathroom being supplied by a cold water storage tank right next to the boiler. There is no problems with the cold water.

The 15mm mains supply to the boiler first of all supplies the CWS from a tee that connects directly with the CWS float inlet valve, then going on to the boiler some feet away. The CWS, boiler and pantry sink are all located in the pantry. Hot water is output to a 'pantry sink' and then kitchen sink on the same floor as well as a bathroom on the floor below. Hot water comes out of the boiler in 15mm but then goes to 22mm pipework for the bathroom below. All hot water taps on both floors are sputtering.

Pity I can't seem to attach a diagram in this forum??

Recently their thermostatically controller mixer shower has had a 30% loss in pressure but had been fine for months so this could be something else. Please see diagram attached.

My view currently is that this is being caused by air getting in from the hots taps in the bathroom below. And what I think might sort it, is to put an NRV on the 22mm hot pipe at as low a point as possible, before it divides to supply the various appliances.

However I am also a bit suspicious of the the short connection to the cold water storage tank. Seem to recollect though that many combi boilers have a way of venting air coming in via its mains supply, so that should be OK. I dont generally get much involved in boilers.

Suggestions or comments welcome

 

[Ermintrude]

Initial thought was syphoning ?

 

[michcosg]

Thanks Ermintrude. Would you elaborate on this a little more?

 

[Ermintrude]

Not enough hot water in pipes so the tap sucks water out rather than it flowing ?

 

[michcosg]

Ah yes sounds good Ermintrude. Any suggestions about how might get around this other than replacing his 22mm pipework with 15mm!?
Note too this problem is also occurring in the pantry and kitchen sinks which as far as I recollect have 15mm pipes running to them - will check the size of the pipework to these tomorrow though and update.

 

[Whyme]

Whats the mains pressure like.. Could it be that when the cws is trying to fill, the hot draw off from the combi can pull air in back through the float valve..Unlikely but just a thought..?

 

[Ermintrude]

Sorry it's a bit difficult without being there. Open one tap at top 1/2 and see if flow is steady? If so fit an anti vacuum valve. - used to fit on old copper unvented

 

[michcosg]

Thanks Ermintrude - will check the top 1/2s pipework and confirm if it is also 22mm - hot taps in top 1/2's kitchen and pantry definitely not flowing steady ie sputtering.

Presumably if I was to fit an anti-vacuum valve, I would fit it close to where the 15mm hot water from output boiler connects to the old 22mm pipe. Possibly even two of them if upstairs and downstairs are separate 22mm branches off the 15mm hot water supply from the boiler?

 

[michcosg]

Thanks also Whyme. Will also bypass the CWS today and see if that improves things.

 

[michcosg]

Having by-passed the CWS, getting no sputtering on the pantry sink, kitchen sink and indeed the basin in the bathroom below. But still getting it on the bath taps below.

Its actually only 15mm to the pantry sink for the last 1 metre+, the other 1 metre + being 22mm With the kitchen sink it is possibly similarly only 15mm for the last 1 metre + (not sure as under floor) with the other 4 metre likely to be 22mm. In the case of the basin in the floor below only about the last 1/2 metre is 15mm.

Thus rather than installing an anti-vacuum valve, what might work and be simpler is just to convert about the last half metre of pipework to the bath to 15mm.

Will let you know what the outcome of this measure is.

For your interest I have also included a definition of an anti-vacuum valve below

Thanks again Whyme

Description
A compact valve designed for use with hot water heaters to
prevent a vacuum forming in installations where there is the
potential of the draw off rate exceeding the rate of flow to
the inlet, this can occur in properties with multiple outlets
below the base of the hot water heater.
The valve contains a check cartridge which under normal
conditions is held closed by the system pressure, when a
vacuum condition exists the suction will cause the check
cartridge to open and air to flow through equalising the
pressure within the hot water heater.

Src: http://www.heatweb.com/pdf/RWC/antivac.pdf

 

[michcosg]

Hi folks

Just an update. Having replaced the 3/4" flexi x 300mm to the bath hot water tap, found that still getting sputtering to this tap.

Note replaced with 3/4" tap conn with 15mm copper tail which then attached some 15mm HEP - 3/4" to 15mm flexi having its seems a 22mm intervening hose.

Note When by-passed CWS on above occassion did not get great seal on by-pass so even though still no sputtering on nearby sink taps, may have contributed to sputtering on hot bath tap below.

Plan: To make a better sealed by-pass and extend lenght of 15mm below to maximum accessible about 1 metre. Otherwise fit 3/4" anti-vacuum valve (£65 from Nabic on-line) at highest point of branch to baths hot tap below. All this is, is of course dependent on the customers authorisation.