Shower reccomendation for combi

[Geoff]

I currently have a mixer shower attached to a Puma combi boiler. We've long since had a problem as we appear to get cycling of the boiler....

What appreas to happen is that the flow rate is insufficient to keep the boiler running all the time so it shuts down, the shower goes cold, boiler cuts in gets hot again, cuts out, goes cold etc. This is not so bad during the winter months as the water entering the house is colder therefore requres the boiler to be on more to heat it etc. However, it gets worse in th summer months. I've tried everything over the years to correct this, changing boiler settings, pressure balancing valves, changing shower head and hose to increase flow rate etc.

I'm now about the change the shower (we want to change it anyway). I was wondering about the best one to pick to remove this problem.

I've been looking at the mira excel which says it is designed for this. Does anyone have any experiences of this and can point me to the best one to achieve max flow rate to get over this....?

Thanks

[John Rumm]

Have you tried leaving a basin tap running a small amount while showering?

Make sure you go for one with controllable flow rate (some are fixed flow and only allow the temperature to be adjusted).

[Martin Pentreath]

Hi Geoff,

Are you sure it's not caused by the secondary heat exchanger being gummed up? The symptoms you describe match. The problem usually occurs when a build up of iron oxide on the primary side (the water that also goes round the rad circuit) makes the exchanger unable to conduct heat through to the secondary side efficiently (ie to the water coming out of the taps). In other words the shower water is not taking heat away from the boiler as quickly as the boiler is supplying it. After a while the water going round the primary circuit gets hot enough for the boiler to cut off on its thermostat. It will cycle like this in the way you describe.

I would have thought for the problem to be caused by the shower not using up water fast enough (as you're guessing) would need a shower of particularly pathetic performance.

If it is the heat exchanger it should be possible to get it out and clean it up.

Cheers!

Martin

[Geoff]

Mmmmm makes sense.... have to investigate. Anyone any idea how easy this is to do on a Potterton Puma 100 boiler?

Hi Geoff,

Are you sure it's not caused by the secondary heat exchanger being gummed up? The symptoms you describe match. The problem usually occurs when a build up of iron oxide on the primary side (the water that also goes round the rad circuit) makes the exchanger unable to conduct heat through to the secondary side efficiently (ie to the water coming out of the taps). In other words the shower water is not taking heat away from the boiler as quickly as the boiler is supplying it. After a while the water going round the primary circuit gets hot enough for the boiler to cut off on its thermostat. It will cycle like this in the way you describe.

I would have thought for the problem to be caused by the shower not using up water fast enough (as you're guessing) would need a shower of particularly pathetic performance.

If it is the heat exchanger it should be possible to get it out and clean it up.

Cheers!

Martin

[Andrew Gabriel]

cuts in gets hot again, cuts out, goes cold etc.  This is not so bad during

changing boiler settings, pressure balancing valves, changing shower head

You need a shower which is designed for combi/multipoint operation. They have much faster acting elements (often some sort of spiral bi-metal rather than a wax pellet), and they are designed to cope with a large and rapidly varying pressure differential between cold and hot inlets. They are also quite a lot more expensive than the cheap wax pellet thermostatic showers.

or hard water scale on the secondary side.

[Martin Pentreath]

Have a search in the google usenet archive under the boiler name, or use it in the title of a new thread, you may get more takers.