Thermostatic Showers and Combi Boilers

Discussion in 'Plumbers' Talk' started by dave93, Nov 9, 2004.

  1. dave93

    dave93 New Member

    I have a thermostatic shower and a combi boiler (I've just moved into this house). The swhower runs fine for a few minutes then shuts down to a dribble. All I can think of is that the boiler isn't sending through constant hot water so the shower thermostat shuts down to save me getting a cold shock.
    Further to this a gas fitter came the other day to fit a new gas main, I was talking to him about it, he didn't know the answer but did say that since he has had a combi boiler fitted he can't get a decent shower on a regular basis.
    Are there some common problems caused by using a combi?
    Thanks Dave
  2. devils advocate

    devils advocate New Member

    Hi D93.

    I've just fitted the same - a thermostatic shower and a combi (GlowWorm CXi) boiler.

    I did note that the shower's instructions included that the hot supply must be at least 60oC for the thermostat to work properly - I think most combis will struggle to supply this temp when almost <u>full-on</u>, so there isn't much room for error.

    Does your shower have a separate flow control, or is it a combined flow/temp control? I'm thinking that if you can reduce the flow rate through the boiler, it'll heat to a higher temp.

    If the shower does have a flow control, try turning it lower. If it doesn't, I wonder if fitting an isolating valve in the hot supply to it, and turning this down a little (to reduce hot flow and increase its temp)might help (you might have to do this to the cold as well to match).

    Bear in mind that these are my thoughts, based on my mum-in-laws's pathetic combi which can only provide a decent hot temp if the hot tap is turned half-off. Thankfully, my shower seems to be working well.

    I wouldn't actually bother trying my idea above unless a Pro confirms it might work...
  3. devils advocate

    devils advocate New Member

    I'm assuming, of course, that your boiler doesn't have an adjustable DHW heat control?

    However, if it does, then try tweaking it up a bit.

    What you need - I suspect - is greater hot water temperature, not actual flow; so if you reduce the flow, the temp should increase.
  4. taffy

    taffy New Member

    I tried to get a combi/thermostatic shower combination to work for 3months gave up in the end and fitted a std shower controller.the thermostat in the boiler fights the thermostat in the shower less flow through the boiler hoter the water shower valve the closes the hot water to the shower head even less water so hotter and hotter get the picture
  5. dave93

    dave93 New Member

    Thank for the input, I was coming around to getting the same answer as you.
    Thanks Dave
  6. blahblah

    blahblah Guest

    Dave, has your boiler got a fully modulating burner? What do your shower and boiler techies say?
  7. dave93

    dave93 New Member

    I havn't spoken to anyone about the boiler apart from the gasman and the people on this forum. I know very little about combi boilers apart from the fact that I beleive that they are like a glorified geyser. How would I know if it has a fully modulating burner? All I know is that you can set the temperatures for hot water & central heating water at the boiler.
    Thanks Dave
  8. devils advocate

    devils advocate New Member

    Since your boiler has a DHW temp control, have you tried turning it <u>up</u> so that your shower gets water at 60o+?
  9. old school

    old school New Member

    I think Taffy was on the right track with this one. You say the shower reduces to a dribble, a cold dribble? if the shower mixer wasnt getting enough hot water it wouldnt shut itself down, that will only happen if there is an excess of hot water so you dont get scalded. Look at it from a different angle, is there a lack of cold water flow? is there a filter in the mixer which is blocked? try turning the temp setting right round to cold and see what the flow is like. another silly question, what is the water level like in the feed tank? if the cylinder cold feed is higher than the cold water service tapping, as is normal, if the ballvalve is blocked maybe you are running out of water. I doubt this is the case but it is another possibility

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