Radiators only tepid

[Markus Splenius]

Hi,

I have a gravity fed hot water system powered by a Baxi Back Boiler (Baxi Bermuda 552) which recently stopped working.

On removing the fire front I could see that the flames were burning yellow and not the expected blue colour. It turned out that the burner bar in the boiler had rusted pretty much to a powder! (The boiler is about 20 years old).

I replaced the burner bar and the flames now look healthy and blue, but the radiators are only getting tepid. The system is full of water (I checked the header tank in the loft) and the radiators are all bled. The boiler is burning constantly.

Could the pump also be broken? It seems to vibrate but does this mean it's actually working?! How can I go about testing the pump?

Another question I have is why does there seem to be only one pipe coming out of the boiler to feed to the radiators? It comes out of the right hand side of the boiler and the splits into two with a T-piece. The T-piece seems to have a direction of flow arrow on it. Is it some kind of clever valve?

Any advice appreciated.

Markus

[Set Square]

How many pipes are there in toto connected to the boiler? - (there are 4 tappings, two each side)

Does the hot water still get hot ok?

Do the radiators get a bit warm in the summer when you have the boiler on just for hot water? If so, you may have some gravity circulation in the heating circuit - and this is perhaps what you have at the moment if the pump has failed.

The pump should have an end cap which unscrews to reveal the end of the shaft (very little water will come out when you remove the cap). You should be able to see the shaft rotating. If it isn't rotating, it may have stuck on a bit of crud and need freeing. Turn it off and rotate it a bit with a screwdiver (there should be a slot for the pupose in the end of the shaft). If it still doesn't rotate, check that it is being fed with 240v - and check the wiring back through the room stat (assuming you've got one) to the programmer. If it's getting 240v but still not rotating, it's time for a new pump. [Providing it has serviceable isolating valves either side, it's not too difficult to change - and doesn't require the system to be drained].

[John]

There are a number of other implications in respect of ensuring the safe working of the boiler such as flueing, ventilation, etc which i hope you have taken care of but lets concentrate on your particular queries for now.

I was distinctly under the impression that the 552 was now obsolete so where did you get the "burner bar"? If it was out of an old boiler unit was it from the same model and rating and has it got the same injector size and burner pressure as your old one?

If the boiler is burning constantly the heat input is not adequate to satisfy the heating load on it.

If the pump is not pumping then heat is not removed from the boiler hance the boiler temperature rises and the burner is switched off by the thermostat so i'd say no its not broken

Its an injector tee. The pumped water circuit enters via one end of the tee and the water flowing across the branch port induces a flow from the branch pipe rather akin to the way a paint sprayer works by blowing air across the suction pipe from the paint resevoir. For a fuller explanation look up the works of Bernoulli and venturis. The baxi is coupled to the primary of the hot water cylinder and heat produces a thermosiphon (gravity circulation system). when the heating circulation pump is running the injector tee encourages the sharing of the boiler heat between the radiators and the hot water.

[Markus Splenius]

It's a genuine baxi spare part. The boilers are obsolete but spares are still available. The only reference I could find to it on the net was here:

my local heating spares company had one in stock.

When I posted the message I wasn't being very observant - the boiler stops burning every few minutes.

Could the injector T be broken or partially blocked in some way?

Is it possible that the heat exchangers at the top of the boiler are not working fully for some reason?

Thanks

Markus

[Owain]

"Markus Splenius" wrote | When I posted the message I wasn't being very observant - the | boiler stops burning every few minutes.

Pump knackered or system badly sludged.

Owain