worcester 35CDI Hot water

[Sammiken]

We have a 35 CDi combi installed about 3 years ago. We also had the water mains supply replaced - new blue polypipe - and flow is great.

Recently, when running the hot water tap, I've noticed that the boiler cuts out after a short while. When the hot tap is running much cooler water (cold!), the boiler kicks in again. (The central heating is OFF.)

A 5 minute shower is interrupted 4/5 time by these cooler water spells.

The boiler has had a service does annually, costing sme £150. I would prefer not to fork out more if there is a simple DIY fix for this.

Any suggestions...

 

[ChrisR]

Could be the HW pump (you have two!) going slow, but more likely is scale in the primary of the domestic hot water heat exchanger. In other words the installer didn't do his job properly. The system should have been flushed according to its age (and the BS's), then inhibitor added.


Only way hard water can be a pest on the primary sid eis if you keep having to "top up" a leaking system.

 

[COG]

If your boiler is 3 years old then it should be a MK1 CDI. The fault diagnostics would pick up an overheating fault and flash the CH and DHW lights slowly if the flame is just dropping out and relighting its usually that the min gas pressure is too high and the boiler cant lower its output to match the demand .No simple solution without expensive test gear best get Worcester out £160.00 will fix any fault other than heat excangers,£94.00 for a service/inspection.Cheaper than your man . check your hot water stat is on max at the boiler then only the stat in the shower will be doing the work.