Main Medway Super Water Heater- little or big problem?

[Mefster]

We have a Main Medway Super water heater which supplies hot water to the house. Recently it has started to run cold after a minute or so of providing hor water. By turning off the hot tap and then starting again it appears to solve the problem (until a minute or so later). The problem is particularly bad first thing in the morning (I imagine when water pressure is low as other households have showers). The shower will run ice cold until another hot tap is run: when this tap finally runs warm, it can be turned off and the shower will again run warm for a minute or so.

Even with low demand and decent water pressure and the temperature turned to the maximum, you can only ever get hand-warm water- no chance of scalding!

Is this a common problem that could be resolved by a simple service or does it sound like something more terminal?

 

[duffin]

probably diaphragm gone.a few quid to buy. or possibly the filter in the water inlet. but I'd go for the diaphragm, seeing as you're having to "jumpstart" the hot by turning on more than one appliance.

 

[mysteryman]

Get it serviced, but forewarn the serviceman that it needs a diaphragm.

 

[Mefster]

Thanks for the replies. Sounds like there's a chance it might be reasonably straightforward to get sorted.

I was thinking of getting British Gas to do the service: they cover our central heating and whenever we've had to call them they've been fast and excellent. At the moment they have an offer where they will do the service for £45, or offer the service and 12 months of cover for a further £55.

Would a diaphragm replacement be straightforward (would I likely just have to pay for the part)? What is a ball park figure for the service and diaphragm change? I'm trying to see if British Gas will be competitive.

Thanks in advance!