Lack of hot water


Postby johnny s » Tue Jun 24, 2008 11:19 am

I've got a Potterton Nettaheat boiler installed when the house was built in 1987. The CH setting works OK (though the boiler doesn't stay on for very long and the house feels cold after a while). The HW circuit fires up the boiler for up to 5 mins but the water doesn't get hot. If I switch the CH on, however, I get plenty of hot water. This is a bit annoying as it means I have to leave 2 rads on to get HW even when its baking hot outside. How can this be fixed??

The system gurgles horrendously and constantly needs bleeding. Would power washing the system fix this?
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Postby plumbbob » Tue Jun 24, 2008 6:45 pm

Describe in more detail what type of heating system you have. Without more info there are just too many options of what could be wrong.
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Postby johnny s » Fri Jun 27, 2008 11:28 am

Its an open vented system. There's a room thermostat & I have 2 TRVs on the rads. The hot water cylinder doesn't have a thermostat and no plumber has yet been able to find a 3-way valve in the system.

With the CH off the bathroom rad stays hot as do one or 2 of the others. I normally isolate them in summer and the HW is OK. This year, doing this means I get no HW so I've had to turn the CH back on and leave 2 rads open so that the pump doesn't dead head.

The CH often needs bleeding but with the current set-up its even worse with the bathroom rad being half full of air every few days and lots of gurgling.
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Postby htg engineer » Fri Jun 27, 2008 11:38 am

Sounds like the primaries are full of limescale and the water is only getting past when the pump is running.

Powerflushing a system of that age is not financially viable. £350+ for a flush is pretty much half price of a standard combi boiler. If it is just the hot water with the problems the radiators and pipeowkr may be ok and just need cleansing and inhibitors adding.

Then after a powerflush, the tank/cylinder coil may be choked. New tank or cylinder ? £350ish

So £700 - you can get a Worcester Greenstar 30si for £738 or a Baxi 105HE for about £650.

Is a new boiler an option for you ? not knowing your financial status it's hard to advise - but i wouldn't waste my money powerflushing.

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Postby johnny s » Fri Jun 27, 2008 2:55 pm

htg, thanks for the great advice a new boiler is definitely an option.

3 plumbers/ central heating guys I've had in the house over the past 10 years have all said I need to power flush the system as the water is black and the bottom of the rads can go cold (when top is hot).
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