Open vented system, No HW, CH works fine, BAXI 80HE boiler shows Dry Fire after every restart

[gazfen]

Really?
This is a boiler model I regularly work on same as combi boilers
This is bread and butter work for me.
When I say a heat only boiler is way to go along with cylinder, I say that from base of experience
If boiler in the post is a nightmare, to repair a combi when it breaks down is going to be suicidal

To repair a boiler one needs to understand operate sequence, need set of tools and skills to work on gas, water, electrical, mechanical and electronics. Being able to join two pipes and hang the boiler on a bracket does not means nothing.

When it comes to a gas boiler, a boiler should be chosen by looking at each site. One boiler make and brand or type does not suit every household

Can see page 10 just round the corner

I’m not having a nightmare lol, could have it fixed in a jiffy. Lol

 

[HERTS P&D]

And we are at page 10!



Andy

 

[DP]

And we are at page 10!



Andy

Indeed.

There are couple of problems here that has brought us to page 10

One is the pros are offering advice not being on site. This will always be difficult and is akin to faultfinding solely based on the end users utterances.

Two. Understanding what is really happening here (remotely)

 

[DP]

I’m not having a nightmare lol, could have it fixed in a jiffy. Lol

What do you think is causing dry fire here.
Can take it to CC if you like
My reply was not aimed at you but reflecting on additional complexity of a combi boiler against a heat only and cylinder setup which I see as a belt and braces setup

 

[gazfen]

usually cold feed blocked, difficult to say without looking at the system, dirty system could be out pal.

 

[Johntheo5]

We know for sure that one reason for the. dry firing was because each time CH was called for then little or no flow because the roomstat was calling with the TRVs manually throttled right down?, I dont think it ever happened when calling for HW or HW& CH. On HW only the flowrate is ~ 9/10 LPM at a 2.9M pump head. One test I would like to see is CH only requested, HW programmed OFF, TRVs opened, roomstat turned up. If the boiler doesnt fire then could be no 230V from the HW OFF contacts to drive the MPV to the CH position.

 

[DP]

We know for sure that one reason for the. dry firing was because each time CH was called for then little or no flow because the roomstat was calling with the TRVs manually throttled right down

What I noticed however is the fact that even though the pipe that feeds the coil in the cylinder is very hot the return pipe from the coil seems to be cold (this only happens when I am blasting the radiators as with CH disabled they never get even luke warm). What I also noticed is the BAXI boiler going into Dry Fire mode in any other setting apart from when I turn the heating on via valves located on the radiators

Dry fire during HW only run

Pipe into the coil is red hot but out of the coil is cold because of restricted flow through the coil. This is an old cylinder that often would have been used for gravity circulation and return having been changed to plastic may have been due to an ongoing issue or be an upgrade to convert to fully pump if originally gravity circulation.

usually cold feed blocked, difficult to say without looking at the system, dirty system could be out pal.

have suggested this and in such cases is the cause.
Have suggested to disconnect at the 3 port and plastic and check into the indirect coil to ensure it is clear


An example of blockage

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[Johntheo5]

How is your system performing now @fandyman and with what pump settings.

@Johntheo5 I've left it on CCII for 2 days now and no problems so far (my wife will kick me out from the house if I go to the loft again ).

Will try to check tomorrow though.

Seems to be circulating through the coil now?

 

[DP]

I’m

Seems to be circulating through the coil now?

Good if it is. Do you think higher pump setting cleared the blockage?

 

[Johntheo5]

I’m

Good if it is. Do you think higher pump setting cleared the blockage?

It was originally at its highest setting, CCIII @ 6M, I suggested CCII @ 3M which I thought might help the MPV to change over, then if this was OK, to change the setting to CP2 @ 4.5M after a few days and maybe finally back to CCIII again but then maybe settle on CP2 @4.5M.

 

[fandyman]

Hi, Sorry as I just partially follow this now but just to clarify that even though I initially suspected there was a blockage it was not the case after I managed to bleed the manual air vent before the coil twice (some air trapped on both occasions). I suspect that what @Johntheo5 advised about the pump running mode and the bleeding of the manual air vent plus powering off and on the system together with manually testing the diverter valve few times seemed to fix the problem for now.

I am still running the pump on CCII and it satisfies my needs so far. Other than that no DRY FIRE on the boiler at all. I also have CH and HW according to my demands now but I have not tested it out to the max yet (not enough time in recent days).