Hot Water Air Lock Conundrum and help

[captfiasco]

Hello

A slightly nervous first post from a non-expert at his wits end....apologies if my terminology betrays my inexperience.

I have a problem with my hot water/central heating that has beaten 2 local engineers and a national organisation.Put simply, during the summer when the gas boiler is heating only the water, the hot water system in my house works perfectly, delivering a good flow to baths and sinks without problem. In the winter when the boiler is working with both the central heating and the water (not necessarily simultaneously) the hot water flow varies considerably, often reducing to no more than a trickle in the upstairs bathroom and the downstairs kitchen sink. It can take up to 30 mins to run the shallowest of baths.

When the hot water flow is reduced it splutters out of all taps indicating, i believe, there is air getting into the hot water system when the central heating is on. The extent of the problem varies day to day (possibly reflecting how cold the day is - a cold day will see the central heating operating more often and cause a bigger problem sooner? Dunno - my amateur speculation!).

Turn the heating off and the air locks will clear and water flow will, over a long time (over night for example), return to normal.

The problem has grown progressively worse and got to the point where we turn the heating on reluctantly because of the impact on the hot water. With winter coming the re-emergence of the problem is becoming a real worry for my partner and I.

The house is 20 years old, average sized, with a single bathroom upstairs and a sink in the downstairs kitchen. There is no shower. The hot water tank is in the airing cupboard upstairs at a similar height to the bathroom. There is a cold water tank in the loft that feeds the hot water system. The ballcock in the cold water tank was changed during an unsuccessful attempt to fix the problem by a local plumber - the tank is fed from the mains and refills quickly (as it does when the system works in the summer).

Air locks i can clear but i would rather they didn't occur at all. Frustratingly neither I nor the heating engineers and plumbers we've called on can work out how air is getting into the hot water system apparently when the heating is on. Assuming of course that air in the system is the problem.

Any thoughts or ideas gratefully received..

Many thanks in advance

 

[Tonycane]

Christ that's random, the heating shouldn't affect your gravity hot water flow/pressure. I would start by completely draining the how water cylinder, remove the top tank tap in and check for scale build up as this can cause a blockage. I would wet vac out all the crud in the bottom of the cylinder too. While it's drained replace the gate valve, might be jammed.

 

[Chalked]

1. How many tanks are in your loft?
What make of boiler do you have and do you fill it through a filling loop?
Can you post a picture of the airing cupboard..?

I'm wondering if the boiler vent has been teed into the hot water vent. This could cause your problem. You would have dirty hot water though!

 

[Last Plumber]

Is this an indirect hot water cylinder which is open vented.

( two tanks in loft or above it somewhere normally one small for heating one larger for CWS to feed cylinder ?).

you didn't mention an f and e tank for the heating ( small one)

It sounds like a primatic that is either failed or supplying a heating system that's too big.

Need more information though, at this stage I'm guessing lots.

Have you for example noticed that your DHW is discoloured ?

 

[Riley]

Was thinking primatic cylinder too. Pics required op

 

[Last Plumber]

Yep, good idea, pics please and include, pipework around cylinder !

 

[Frog67]

Fully Pumped system or Pumped Central Heating and gravity Hot Water?
Also Boiler make and Model please?

 

[captfiasco]

Thank you for all your replies, not sure i got all the acronyms but i'll have a go at answering the questions.

It is a baxi gas boiler first fitted when the house was built in 1997. There are 2 tanks in the loft, one a large cold water tank that I believe feeds both the hot water and upstairs cold taps. Also a smaller one that I assumed was a central heating header tank. The hot and cold water is clear.

The temperature of the fully heated hot water is the same regardless of whether the it HW only or HW+CH running. I did wonder whether a fault in the boiler meant the hot water was heated to a higher temperature when the HW+CH was running, this could have created vapour bubbles that accumulated to form an airlock. Turning off the CH would have allowed the water too cool and the vapour to condense back removing the airlock. Measuring the temperature shows it to be always the same and broadly aligned with the hot water tank thermostat so probably not that. Probably a daft thought both that's rusty schoolboy physics for you

Here are the pictures hope they show what you were looking for.

 

[Last Plumber]

At the moment I can only think that it is piped incorrectly.

I suggest you get a Heating Engineer to come and take a look over it.

It would be worth paying for a couple of hours time to solve this in my opinion.