Radiators warm but not hot enough. All bled??

7 Oct 2011
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United Kingdom
Hello everyone very new to this forum and would really appreciate any help massively.

I have a very old SIME combi boiler in my flat. I think it was one of the first out many years ago. I have piping hot water through my taps and my gas fed shower. I have no room thermostat but have a thermostat for hot water /central heating plus timer on the boiler. The thermostats are at max.

The central heating radiators are "warm" to touch not scalding hot like they used to be. I have bled all the radiators, left them on for hours and hours and the heating is, well, pathetic.

I have lived with the problem long enough and don't fancy another cold winter. Last winter I used the heating but it cost me a packet which I don't mind but I was still freezing which is why it went off. The weather is really getting colder and I want to enjoy my house for a change over the festive period.

This problem has been a long standing issue. I have been told it could be the boiler heat exchanger, needing descaled and central heating radiators needing a flush. I myself don't go for the heat exchanger as why would the hot water via taps and shower be scalding. Surely if it can do this why can't it heat the radiator water. Ok it may need a flush but I am not convinced, it may just be a waste of time and money.

I really don't want to replace the boiler which I know is ancient because it does the hot water so well and I have been told it could cope with more radiators which I would like at least one more of in my loft room/bedroom.

I would be extremely thankful for any advice to help resolve it soon so I can get someone up to fix it and sound like I know what I'm talking about.

Apologies for the length. Am getting desperate and typically don't trust any workmen from hard bitter experience.

Thanks everyone ! :D :D
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yes, of course you can get ripped off, maybe the system does need a flush - did the problem just happen one day or over a time?

the HE might well also be on it's way out or clogged.

you might try a diy power flush - drain down, shut valve on each rad, take the rad outside and flush through with a hose till the water runs clear - banging the bottom part of the rad with a rubber mallet to dislodge any aggregations. how old are your rads by the way? they corrode through eventually............

it's fair to say a new boiler won't last as long as your old one, but it'll be massively cheaper to run and you can get your system properly cleaned with new trvs into the bargain - better than spending handfulls of cash after handfulls of cash without knowing if it'll solve your problems.
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Which Sime abortion are we dealing this time? Might there be a filter on the return that is clogged? Could the diverter be stuck in hot water mode? Could the heat be short circuiting trough an internal by-pass.

What happens if you turn off all but one rad? Does it get proper hot?

All these questions - so little time.

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