Combi boiler blowing hot and cold

origrudeboy

Please help

I have had six months of pleasure out of a new MIRA combiflow shower. My house did not have a shower previously.

This week, the water started regularly running cold, warm up again and go cold again.

I checked the sink hot taps and it is happening there as well.

The boiler is not reporting any error messages. This appears to have happened out of the blue.

Any suggestions for what has gone wrong?

Thanks in anticipation.

Porker

have you got a 'warm start' type setting on the system - if you have it could be this kicking in coupled with a failed diverter valve, so the system is trying to give you cold only but the warm start can give you odd bursts of hot water. Just a thought, similar happened to me recently. Have you recently just turned your central heating back on by any chance?

robowen

what make and model boiler have you got ??

origrudeboy

At work so I'll have to get the modle info tonight

just wanted to say great clip, robowen. That is one of the best Jim Carrey clips ever, have you seen his Vanilla Ice spoof

robowen

origrudeboy wrote:

At work so I'll have to get the modle info tonight

just wanted to say great clip, robowen. That is one of the best Jim Carrey clips ever, have you seen his Vanilla Ice spoof

Thanks !
No....not seen that one.

You wouldn't believe how many frames I had to take out of this clip to use it as an avatar in MSE.com :rotfl:

rob

gundo

origrudeboy wrote:

This week, the water started regularly running cold, warm up again and go cold again.

I checked the sink hot taps and it is happening there as well.

I have and have had exactly the same problem. It's due to the boiler overheating and shutting off.

Here's what happens to me (we have a combi boiler and shower running off it):

1. Run shower, hot water gets warm then gets hot.

2. To keep the shower water temp comfortable you add cold water.

3. Reduced cold water input to boiler means that less water is going through it so it's temp gets still hotter.

4. You add more cold water to the shower mix. Water flow through boiler further reduced so temp rise from inlet to outlet of boiler still greater.

5. Eventually the boiler just isn't getting enough water flow through it and it gets too hot and shuts off for safety.

6. Shower gets cold. You shut off cold water in shower mix in an attempt to get it warmer.

7. Boiler gets more cold water flow through it so switches back on.

Repeat ad infinitum.

It happens worse in summer as the inlet water temp is higher to start with so the outlet temp is higher and the boiler more easily overheats.

SOLUTION

If you boiler has a water temp control then you could turn this down. Ours hasn't. We get the boiler heat exchanger descaled as this is the real problem. If the exchanger is scaled up then the flow through the boiler is reduced so the water gets gets hotter.

Hope that helps you.