New central heating - gurgling & running water noises

Postby dslawton » Wed Nov 19, 2008 11:00 am

Hi all,

I have a query that may or may not be a major problem but I'd very much appreciate some expert advice to be sure.

I recently had my central heating boiler replaced. As it was previously an old gravity fed system it was also converted to fully pumped with the pump and electrics moved upstairs to the airing cupboard. Also had thermostatic values fitted to all rads except for bathrooms and hallway, where the wireless room thermostat is sited.

Some extra info :
• New boiler is a Potterton Promax HE Plus condensing boiler, fitted downstairs in kitchen (same site as old boiler)
• Boiler thermostat set to almost max
• Hot water tank stat set to 60 deg
• Motorised 2-way valves fitted on each of radiator and hot water circuits below pump in airing cupboard
• Pump speed on max (engineer said to leave this way)
• Gate valve in between motorised valve and hot water tank (turned about half way on/off)
• Heating system is microbore (house is late 70's build) with rad feed pipes under floorboards upstairs and in concrete floor downstairs
• 6 rads upstairs 5 downstairs
• System had full flush prior to new boiler install

First of all the good news. The effectiveness of both the central heating and the hot water is excellent. Certainly radiators are much hotter and heat up much more quickly than with the old system. All radiators get hot and there aren't any cold spots. Hot water also fine. So I have no complaints with this at all.

My query is with the noises, of which there a few which may or may not be related :

1. When the boiler fires upon timer coming on and request for heat from the radiators, there is what I can best describe as a gushing and gurgling of water from all around the pump area. Now I know the pump will obviously make a noise when it starts up but it seems to be all around the piping gurgling for quite probably 10 seconds. Can be quite loud. No banging just gurgling and glugging. Noticeably worse on initial morning start up from cold when the odd glugging sounds can go on for half hour or so. Eventually goes away once warmed up but also then gurgles, albeit less, when boiler kicks in again when further request for heat.

2. Trickling water sound down the radiator hot feed pipe from pump leading to downstairs radiators. Can get quite loud (like tap running). Only makes noise when downstairs rads are warming up (i.e. no noise until upstairs rads are hot and downstairs rads then get heat. No noise when heating switches off)

3. Water trickling sound coming from pipes going in/out boiler, again like a tap running slowly

I only get the sounds when the heating circuit is running (i.e. it's fine when just hot water cirtcuit)

So my obvious first thought was air in rad cirtcuit so bled all the rads. Which were fine. Tried isolating to a single rad and bleeding. No air all fine. Bled pump by loosening screw in centre, also fine. Also checked header tank in loft to make sure it had water and water was on. Fine again. I also tried different pump speed settings, no change.

So I called the company who fitted it, who have been helpful and came out to inspect right away. They checked various things but pretty much said its working fine and that the noises would eventually go away.

I guess my expectation was for a system that was quieter than the old one rather than noisier, but this isn't the case.

Any advice very much appreciated. Thanks!
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Joined: Wed Nov 19, 2008 10:59 am


Simply Build It

Postby plumbbob » Thu Nov 20, 2008 10:23 pm

I can't see anything wrong with the installation other than the noise you describe. Basically, I agree with nearly all the points the engineer has said other than the explanation of the noise.

Obviously, the noise is caused by trapped air. The question is is why is it still there. It is often the case that new installations take a while for air to be completely expelled from the system, but the time scale is probably hours / days not weeks.

The first thing to check is to ensure no air is being drawn in down the expansion pipe. Something that is a common fault. The system feed and expansion pipes must be close to each other. If they are far enough apart to be on either side of the pump or opposite sides of the cylinder or boiler, then the fault you describe may occur.

If they seem fine, probably the air is just simply trapped and can't escape. Some part of the system needs to be opened to allow the air to vent.
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Postby dslawton » Fri Nov 21, 2008 1:49 pm

Hi there, thanks for your response.

After it was installed I was kind of expecting the air to be eventually reach one or more of the rads, but it hasn't done and these all seem perfectly fine.

One thing I noticed (after reading the pump installation instructions) is that the pump is mounted vertically and pumping downwards - something it recommends you don't do without fitment of an air release valve somewhere above it, which I' pretty sure I don't have. Dunno whether this would cause my symptoms though.

The cold feed and vent are definitely not on opposite sides of the pump, but neither are they close together - I can see that the vent comes from a 'T' connected vertically just above the pump feed pipe, but I can't see that the cold feed is connected to the same pipe anywhere in the airing cupboard. I'll double check though and also see if air is being drawn in and send the results...

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Joined: Wed Nov 19, 2008 10:59 am

Postby dslawton » Tue Nov 25, 2008 9:26 pm

Hi there

I checked the pipework this evening. The order on the feed pipe from boiler is expansion, cold feed, pump. The expansion pipe and cold feed are more than 150mm apart, more like 300mm. I did the "glass of water under the expansion pipe" test and then switched on the heating & pump - drew in probably around half a pint.
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Joined: Wed Nov 19, 2008 10:59 am

Postby plumbbob » Wed Nov 26, 2008 9:13 am

That's a good idea with a glass of water - must remember that one.

Nothing should be sucked up or expelled out of the expansion pipe, so whatever water is drawn up, it will be worse with air.

The F&E need to be much closer together. Just a few inches is best.

The best position for the pipes is at an elbow in the flow pipe. The elbow replaced with a tee, and connected to the expansion. The cold feed should be fitted to the vertical section just under the tee. This arrangement ensures any air passing this corner in the flow will be diverted up the expansion without any assistance and when initially filling the system, the incoming cold water will not hinder the escaping air.

If the air is left circulating the system, the oxygen it contains will corrode your new boiler (new condensing boilers are susceptible to this) along with the rest of the system. The resulting sludge will eventually restrict flow and reduce the efficiency of the whole system.
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