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Baxi Combi fault

Hello, before I get somebody in, I would like to understand what the fault is. Anybody familiar with combis?
1. pressure is 1.7bar
2. CH appears to be ok (first time I've tried it since Spring); pressure is a stable 1.5bar
3. DHW is where we have a problem; after (cold) bath boiler "Flame failure" and "Safety thermostat" lights both flashing; after reset , its working ...sort of
3a. as water is heating pressure is 2.25bar; as temp builds the pressure starts to waiver (judders between 1.5bar and 2.5bar) and sounds wrong. Issue with DHW pressure differential value?

Comments

  • Alex1983
    Alex1983 Posts: 958 Forumite
    What model is it? When you run the water does in work at all or just got to the lockout lights?
  • grumpycrab
    grumpycrab Posts: 5,043 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Bake Off Boss!
    Alex1983 wrote: »
    What model is it? When you run the water does in work at all or just got to the lockout lights?
    Its a 105E. Since resetting I haven't seen the lights; it does work until temp of water gets high; that's when the pressure starts to judder and the boiler itself is making a strange noise. As if there's a DHW blockage (but only when the water gets hot). Or perhaps a valve isn't openning enough...
  • Alex1983
    Alex1983 Posts: 958 Forumite
    Before it cuts out does the flame light cycle on and off giving you fluctuation in water temperature.

    Sounds like a restricted plate heat exchanger to me.
  • grumpycrab
    grumpycrab Posts: 5,043 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Bake Off Boss!
    Alex1983 wrote: »
    Before it cuts out does the flame light cycle on and off giving you fluctuation in water temperature.

    Sounds like a restricted plate heat exchanger to me.
    Yes, the flame light does cycle; that's been a symptom of this boiler for a while (water never runs at a contant hot temp).Is that a clean out job or a new heat exchanger do you think? Thanks by the way. PS CH appears to be ok.
  • Alex1983
    Alex1983 Posts: 958 Forumite
    Yes certainly sounds like blocked plate heat exchanger. Clean out with a acid cleaner or replace, to be honest there only about £50 for a new one so probably worth replacing. Would be worth investing in a magnet system filter hopefully that will stop it happening again.
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