Baxi 105E Combi - very limited hot water

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18 Dec 2012
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Location
Brecknockshire
Country
United Kingdom
Guys.

I have a Baxi 105E combi boiler. For a month or two I've had issues with my hot water.

I have a good understanding of the boiler and how it works, although no gas engineer I am into air conditioning so know the basics of a heating system.

The boiler preheats the DHW reserve as it should do according to the manual.

When I turn on an outlet I get nothing, warm for a few seconds.
When a hot water tap is on the burner ignites and goes out after 30 seconds, 30 seconds later it reignites. Water temperature is tepid. I don't believe that the water that is preheated gets anywhere close to the tap!

When central heating mode is selected the heating comes on after hot water is no longer called for. The heating works fine.

The HW microswitch is engaged when a tap is open and there is
continuity across it. I also see the diverter valve head operating as I belive it should (I tested with a multimeter and got 240V).

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.


I'm totally lost, any advice would be appreciated.

Des
 
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Guys.

I don't believe that the water that is preheated gets anywhere close to the tap!

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.

Des

The preheated water should go nowhere near the domestic hot water, its primary water!

Although you did not mention it, you obviously have an "Instant" model.

A DIYer should never open the combustion chamber and certainly not charge the primary heat exchanger.

The obvious advice is to call a competent boiler engineer who will diagnose the small fault with your boiler and check it for safety.

Tony
 
Guys.

I don't believe that the water that is preheated gets anywhere close to the tap!

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.

Des

The preheated water should go nowhere near the domestic hot water, its primary water!

Although you did not mention it, you obviously have an "Instant" model.

A DIYer should never open the combustion chamber and certainly not charge the primary heat exchanger.

The obvious advice is to call a competent boiler engineer who will diagnose the small fault with your boiler and check it for safety.

Tony
 
Guys.

I don't believe that the water that is preheated gets anywhere close to the tap!

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.

Des

The preheated water should go nowhere near the domestic hot water, its primary water!

Although you did not mention it, you obviously have an "Instant" model.

A DIYer should never open the combustion chamber and certainly not charge the primary heat exchanger.

The obvious advice is to call a competent boiler engineer who will diagnose the small fault with your boiler and check it for safety.

Tony
 
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Guys.

I don't believe that the water that is preheated gets anywhere close to the tap!

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.

Des

The preheated water should go nowhere near the domestic hot water, its primary water!

Although you did not mention it, you obviously have an "Instant" model.

A DIYer should never open the combustion chamber and certainly not charge the primary heat exchanger.

The obvious advice is to call a competent boiler engineer who will diagnose the small fault with your boiler and check it for safety.

Tony
 
Guys.

I don't believe that the water that is preheated gets anywhere close to the tap!

I replaqced the primary heat exchanger aweek ago thinking that this was the issue, obviously not to my expense.

Des

The preheated water should go nowhere near the domestic hot water, its primary water!

Although you did not mention it, you obviously have an "Instant" model.

A DIYer should never open the combustion chamber and certainly not charge the primary heat exchanger.

The obvious advice is to call a competent boiler engineer who will diagnose the small fault with your boiler and check it for safety.

Tony
 
Tony,

Many thanks for your reply and apologies it was the secondary HE I changed, I was thinking there mayt have been a partial blockage oin it.

If the issue was gas related I'd not venture that far, from what I see though there should be no reason for the fault to lie in the combustion chamber.

Could the issue be as simple as a fault on the DHW sensor?

Des
 
I only see one of that model every two years or so and work it out by seeing it. That makes it difficult for me to advise you as I dont need to remember all the details about them.

You cannot assume the div motor is working just by saying it has a supply! The supply has to be on the correct two terminals and it has to move its thrust pin to the appropriate position. You need to remove the head and see if its really doing that. Try the boiler with the motor removed!

Its so easy to measure the resistance of the sensors. Should be about 13k with the boiler cold.

Tony
 

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